Replace device ID with a random UUID. Add "os" property.

src/com/mixpanel/android/util/Installation.java

@@ -0,0 +1,57 @@
+package com.mixpanel.android.util;
+
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.UUID;
+
+import android.content.Context;
+
+// class that maintains a UUID to track this particular installation of the host app
+//
+// adapted from http://android-developers.blogspot.com/2011/03/identifying-app-installations.html
+//
+public class Installation {
+    private static String sID = null;
+    private static final String INSTALLATION = "INSTALLATION";
+
+    public synchronized static String id(Context context) {
+        if (context != null && sID == null) {  
+            File installation = new File(context.getFilesDir(), INSTALLATION);
+
+            try {
+                if (!installation.exists()) {
+                    writeInstallationFile(installation);
+                }
+
+                sID = readInstallationFile(installation);
+            } catch (Exception e) {
+                throw new RuntimeException(e);
+            }
+        }
+
+        return sID;
+    }
+
+    private static String readInstallationFile(File installation) throws IOException {
+    	if (installation != null) {
+	        RandomAccessFile f = new RandomAccessFile(installation, "r");
+	        byte[] bytes = new byte[(int) f.length()];
+	        f.readFully(bytes);
+	        f.close();
+	        return new String(bytes);
+    	}
+
+    	return null;
+    }
+
+    private static void writeInstallationFile(File installation) throws IOException {
+    	if (installation != null) {
+	        FileOutputStream out = new FileOutputStream(installation);
+	        String id = UUID.randomUUID().toString();
+	        out.write(id.getBytes());
+	        out.close();
+    	}
+    }
+}