In my search to optimize (again and again) Sharingfoto.com, I discovered a great optimization tips by thinkVitamin. Here’s a quote:

When building out your AJAX application, it’s a good idea to keep in mind the different sources of latency that can slow down the user experience. These include:

1. The Database (both in memory and filesystem swap)
2. App Server Execution & Rendering
3. The Webserver
4. The Network
5. The Browser (only in really complex AJAX apps)

Read it and do it!