Asp.net Ajax Gotchas

Today I took a foray into asp.net's Ajax controls.
Mostly it was incredibly simple, however given Microsoft's penchant for surprises, I managed to 2 surprises.
 
I'm using Ajax to pull back a fresh copy of the session variables and display them in an

on the sidebar.
• Generating  an Ajax partial postback clientside
• Some web pages will advocate __doPostBack('UpdatePanel1','');
• This breaks if you have eventValidation on
• Turn off event Validation at the risk of security is my guess?
• Some web pages will advocate using a hidden button and using javascript to trigger it
• This was the approach I got to function without an exception
  
• Response.Write is not allowed in an Ajax partial update
  
• <%= %> seems to have partially worked, but I think it's stripping my html tags