I'm a Thesis guy. Have never regretted it and never looked back.

Me too. I like being able to tinker with it when needed and change the look of the theme completely.

A quality theme is something that bloggers should definitely invest in. It is well worth the money. It is akin to a good logo. It is just something that you should bite the bullet and pay for. It is a great investment. 

I'll second that.  A free theme might seem good at the beginning, but it's better to have one that sticks around and continually improves their product!

I've only been blogging for a few months, so I don't have much to compare, but it seems as though the StudioPress themes have great functionality. For a 3 month old site, I often land on page one or two in Google searches and have achieved a PageRank of 2. Aside from the great SEO, they also look pretty good.

Seems like you made a good choice!

If You Can Read, You Can Cook has a custom theme designed by myself and my brother. That site seems to do pretty well, SEO-wise. It's been growing gang-busters lately.

Unfortunately, when I started blogging, I didn't know better and picked one based on how "cool" it looked.  Unfortunately, the theme I picked was a "Beta Theme", and no longer supported.  It was such a bad theme that it never even made it to a "production level" theme.  Oh I thought it looked cool, and was happy with it at first, but within the past year, I started looking at the SEO configuration, and realized that it was making so errors that may have slowed my growth over the years!

Don't make the same mistake that I made!  Get a production level theme!

Caveat Emptor!!!

Don