Hi,
Im also having problems with the +1 button on my google site and IE8.
The click count doesn't show and when I click on the button, only this error shows:

Webpage error details

User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
Timestamp: Thu, 6 Oct 2011 06:38:14 UTC

Message: Element not found.

Line: 79
Char: 223
Code: 0
URI: https://plusone.google.com/_/apps-static/_/js/plusone/p1b,p1ctrl/rt=j/ver=GxMNp1o6j4A.en_GB./am=!7JOAhqK991xUvfkp/d=1/