[Catalyst]

After spending a lot of time looking around for a way to call a function after an UpdatePanel completes its asynch postback I found that most of the advice revolved around using the Page.ClientScript.RegisterStartupScript function which I just couldn't get working and wasn't excited about in the first place.

Eventually I found the following javascript syntax which was much easier and works great

Sys.WebForms.PageRequestManager.getInstance().add_endRequest(foo);

where foo() is the function you want called after the postback is complete. My need for it was that I'm using thickbox to show the contents of the UpdatePanel but the panel was being rendered by thickbox before it was updated, thus it was always behind by one update.