The IEBlog reports that IE7 has been locked down for shipping and they list all of the CSS changes/fixes they've made. Some include:
Peekaboo Bug
Internet Explorer and Expanding Box Problem
Quirky Percentages
Line-height bug
Border Chaos
Disappearing List-Background bug
Guillotine Bug
Unscrollable Content bug
Duplicate Characters Bug
IE and Italics
Doubled Float-Margin bug
Duplicate Indent bug
Three pixel text jog
Creeping Text bug
Missing First letter bug
Phantom box bug
There's lots more listed too, so if you're waiting to see what's being fixed in IE, check it out.
