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.
I usually write blog posts and my private plain text notes in Markdown using the PHP Markdown Extra flavour which adds syntax for very useful features like tables and footnotes. It is a pretty clean markup language that makes WordPress writing a bit more comfortable than with either Visual or HTML, the two standard post editors.
Try to zoom in or out and see how beautifully the formula scales. It is even (to some extent) copy-pastable.