I just converted my highly unpopular blog, The Moderate Fringe from MoveableType to WordPress. I used the metaldream style sheet, though I did customize it a bit. I also tossed in the authority-image plugin to prevent comment spamming. Other than some differences in style I had to fix by hand, everything went smoothly.
I'm still tweaking the style a bit, but all-in-all, I'm quite happy with the results.
Oh, before anyone criticizes me for not creating my own stylesheet from scratch -- I'm a computer geek, not a designer. I know the technical side of working with stylesheets, I just don't have the artistic eye necessary to create a pleasing look.