IE8 is almost like two different browsers – one in the backward compatibility mode, and the other in standards compatibility mode. The unfortunate part is the IE8 using the compatibility view is not the same as its predecessor IE7. There is a good news that IE8 is CSS 2.1 compliant and that it does offer a standards mode. IE8 is fighting to be standards compliant as well as supporting its past versions, which might create a lot of problems for everyone involved.
However, IE8 team is doing its best to make them work and help developers identify issues, the reason I think this problem will never be solved because of this approach:
We see the majority of compatibility issues in IE8 Standards Mode. Most of these occur when sites expect legacy behavior that no longer exists in IE8 Standards Mode. Upgrading your site to run in IE8 Standards Mode is the best option in the long run, but in the interim you can quickly fix these types of issues by running your site in Compatibility Mode.
Somehow I think the quick-fix solutions will be more popular. I really wish that Microsoft starts separating its past versions from the modern standards compliant version. Otherwise, we are going from supporting 4 different versions of IE – IE8 as two browsers, there is IE7 and yes, IE6 is still alive!