Go to border-radius.com and see how many different code it takes to get a rounded-corner to work on all browsers. Completely agree, browser-specific prefixes are very messy.
A few thoughts followed by a discussion on how various things are done on the 2010 Theme. Completely agree with “Widgets are not List”. It can result in many nested lists that are hard to CSS and I don’t see a good semantic reason why you should build a widget area (or sidebars in general) as a List. I mean sure they are a list of Widgets, but the main content area is also a list of posts; do you want to wrap that in a <ul> as well?
perfect list!