When WordPress 3.2 came out, I switched to the new default Twenty Eleven theme. It works well and looks great, but hopefully I will find some time someday to personalise it a bit. For now I use it almost without modifications.
I do not know a lot about either WordPress or CSS, but I discovered one little thing that seems like a bug: When viewing a single post, the meta links in the top (like the date on a post or the full-size link and post link on an attachment page) are not clickable — at least on Opera, Firefox and Chrome. It seems to work in IE.