When IE8 came out, we decided to put our website into IE7 compatibility mode due to the presence of hacks in the site that we are dependent upon. It has been quite a while, but I remember in particular the min-width hack as explained at http://www.cssplay.co.uk/boxes/minwidth.html
In any case, I am wondering what people do about staying in IE7 compatibility mode. On the one hand, it would seem that as IE7 diminishes, why not move on to IE8 standard? And have less to hack for new pages? On the other hand, right now we only have one mode that handles both IE8 and IE7 - the IE7 compatibility mode. If we took the website out of IE7 compatibility mode, then we are in effect adding another browser to support as we still would want to work for IE7.
Right now we support 5 browsers: IE7 compatibility mode, Firefox, Safari, Firefox on the Mac (different because of font differences), and Chrome. By seeming to "move forward" by dropping IE7 compatibility mode, we then add one more: IE8.
Something else that would be helpful would be a reference to a good list of the differences between IE8 and IE7 compatibility mode.
It appears that http://blogs.msdn.com/b/ie/archive/2009/03/12/site-compatibility-and-ie8.aspx
may answer this question, in which case that part of this question would be answered.