I found this great article in the Geeks With Blogs feed this morning. It talks about an issue with running simultaneous UpdatePanels. The first update gets canceled by the second. They explain how to get around this.
If you ever try to do more than one simultaneous partial update with Asp.net Ajax Update Panel, I guess you already found that Asp.net Ajax Framework cancel the current update request and start the new one. You think I am kidding? Okay lets try the following code: