Index: src/wmsplugin/Cache.java
===================================================================
--- src/wmsplugin/Cache.java	(revision 0)
+++ src/wmsplugin/Cache.java	(revision 0)
@@ -0,0 +1,137 @@
+package wmsplugin;
+
+import java.awt.image.BufferedImage;
+import java.io.File;
+import java.io.FileFilter;
+import java.util.Date;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.TreeMap;
+import javax.imageio.*;
+
+import org.openstreetmap.josm.Main;
+
+
+public class Cache {
+    final File dir;
+    // Last 5 days
+    private final long expire = Main.pref.getInteger("wmsplugin.cache.expire", 1000*60*60*24*5);
+    // 40 MBytes
+    private final long maxsize = Main.pref.getInteger("wmsplugin.cache.size", 1000*1000*40);
+    private boolean disabled = false;
+    // If the cache is full, we don't want to delete just one file
+    private final int cleanUpThreshold = 20;
+    
+    Cache() {
+        this(Main.pref.getPreferencesDir() + "plugins/wmsplugin/cache");
+    }
+    
+    Cache(String working_dir) {
+        // Override default working directory
+        this.dir = new File(working_dir);
+        try {
+            this.dir.mkdirs();
+        } catch(Exception e) {
+            // We probably won't be able to do anything anyway
+            disabled = true;
+        }
+        
+        if(expire <= 0 || maxsize <= 0)
+            disabled = true;
+    }
+    
+    public BufferedImage getImg(String ident) {
+        if(disabled) return null;
+        try {
+            File img = getPath(ident);
+            if(!img.exists()) {
+                //System.out.println("Miss");
+                return null;
+            }    
+            if(img.lastModified() < (new Date().getTime() - expire)) {
+                img.delete();
+                //System.out.println("Miss");
+                return null;
+            }
+            //System.out.println("Hit");
+            return ImageIO.read(img);
+        } catch(Exception e) {
+            System.out.println(e.getMessage());
+        }
+        //System.out.println("Miss");
+        return null;
+    }
+    
+    public void saveImg(String ident, BufferedImage image) {
+        if(disabled) return;
+        try {
+            ImageIO.write(image, "png", getPath(ident));
+        } catch(Exception e){
+            System.out.println(e.getMessage());
+        }
+        
+        // Clean up must be called manually
+    }
+    
+    public BufferedImage saveImg(String ident, BufferedImage image, boolean passThrough) {
+        saveImg(ident, image);
+        return image;
+    }
+    
+    public void cleanUp() {
+        if(disabled) return;
+        
+        TreeMap modtime = new TreeMap<Long, File>();
+        long time = new Date().getTime() - expire;
+        long dirsize = 0;
+        
+        for(File f : getFiles()) {
+            if(f.lastModified() < time)
+                f.delete();
+            else {
+                dirsize += f.length();
+                modtime.put(f.lastModified(), f);
+            }
+        }
+        
+        if(dirsize < maxsize) return;
+        
+        Set keySet = modtime.keySet();
+        Iterator it = keySet.iterator();
+        int i=0;
+        while (it.hasNext()) {
+            i++;
+            ((File)modtime.get(it.next())).delete();
+            
+            // Delete a couple of files, then check again
+            if(i % cleanUpThreshold == 0 && getDirSize() < maxsize)
+                return;
+        }
+    }
+    
+    private long getDirSize() {
+        long dirsize = 0;
+        
+        for(File f : getFiles()) 
+            dirsize += f.length();
+        return dirsize;
+    }
+    
+    private File[] getFiles() {
+        return dir.listFiles(
+            new FileFilter() {
+                public boolean accept(File file) {
+                    return file.getName().endsWith(".png");
+                }
+            }
+        );
+    }
+    
+    private String clean(String ident) {        
+        return ident.replaceAll("[^a-zA-Z0-9]", "");
+    }
+    
+    private File getPath(String ident) {
+        return new File(dir, clean(ident) + ".png");
+    }
+}
\ No newline at end of file
Index: src/wmsplugin/WMSGrabber.java
===================================================================
--- src/wmsplugin/WMSGrabber.java	(revision 13558)
+++ src/wmsplugin/WMSGrabber.java	(working copy)
@@ -25,6 +25,7 @@
 
 public class WMSGrabber extends Grabber {
     protected String baseURL;
+    protected Cache cache = new wmsplugin.Cache();
 
     WMSGrabber(String baseURL, Bounds b, Projection proj,
             double pixelPerDegree, GeorefImage image, MapView mv, WMSLayer layer) {
@@ -75,6 +76,9 @@
     }
 
     protected BufferedImage grab(URL url) throws IOException {
+        BufferedImage cached = cache.getImg(url.toString());
+        if(cached != null) return cached;
+    
         HttpURLConnection conn = (HttpURLConnection) url.openConnection();
 
         String contentType = conn.getHeaderField("Content-Type");
@@ -86,7 +90,8 @@
         InputStream is = new ProgressInputStream(conn, null);
         BufferedImage img = ImageIO.read(is);
         is.close();
-        return img;
+        
+        return cache.saveImg(url.toString(), img, true);
     }
 
     protected String readException(URLConnection conn) throws IOException {
Index: src/wmsplugin/WMSLayer.java
===================================================================
--- src/wmsplugin/WMSLayer.java	(revision 13558)
+++ src/wmsplugin/WMSLayer.java	(working copy)
@@ -175,6 +175,8 @@
                     executor.submit(gr);
             }
         }
+
+        new wmsplugin.Cache().cleanUp();
     }
 
     @Override public void visitBoundingBox(BoundingXYVisitor v) {
Index: src/wmsplugin/YAHOOGrabber.java
===================================================================
--- src/wmsplugin/YAHOOGrabber.java	(revision 13558)
+++ src/wmsplugin/YAHOOGrabber.java	(working copy)
@@ -20,6 +20,7 @@
 
 public class YAHOOGrabber extends WMSGrabber{
     protected String browserCmd;
+    protected Cache cache = new wmsplugin.Cache();
 
     YAHOOGrabber(String baseURL, Bounds b, Projection proj,
             double pixelPerDegree, GeorefImage image, MapView mv, WMSLayer layer) {
@@ -30,11 +31,15 @@
     }
 
     protected BufferedImage grab(URL url) throws IOException {
-        ArrayList<String> cmdParams = new ArrayList<String>();
         String urlstring = url.toExternalForm();
         // work around a problem in URL removing 2 slashes
         if(!urlstring.startsWith("file:///"))
             urlstring = urlstring.replaceFirst("file:", "file://");
+            
+        BufferedImage cached = cache.getImg(urlstring);
+        if(cached != null) return cached;
+        
+        ArrayList<String> cmdParams = new ArrayList<String>();
         StringTokenizer st = new StringTokenizer(MessageFormat.format(browserCmd, urlstring));
         while( st.hasMoreTokens() )
             cmdParams.add(st.nextToken());
@@ -49,6 +54,6 @@
             throw new IOException( "Could not start browser. Please check that the executable path is correct.\n" + ioe.getMessage() );
         }
 
-        return ImageIO.read(browser.getInputStream());
+        return cache.saveImg(urlstring, ImageIO.read(browser.getInputStream()), true);
     }
 }