Since the day we upgraded to 3.x, our customer's started to complain about performance issues.

After some profiling, we found that the application was about 30% - 40% slower due to the following css selector in ext-all.css :

.x-color-palette em:hover, .x-color-palette span:hover{
    background-color: #deecfd;
Page speed says :

Rules that use the :hover pseudo-selector on non-anchor elements. This can cause performance problems in Internet Explorer versions 7 and 8 when a strict doctype is used.
Removing this single line from our project's stylesheet solved the problem.

55% of our customer's are on ie6 ie7, so please remove this crap from the ext-all.css !

Thank you for your attention.