"Please share your thoughts with the community and try to be unbiased as possible."
Its simple for me. I'm an utter noob with great ambitions. I found Thesis first - most promoted, I guess. Actually played around with a pirated version (a friend who had purchased emailed me a copy) and didn't like the feel of stealing and didn't want to buy it based on untested skills. Not to mention the Thesis site itself doesn't validate :(
Then I found Hybrid. Ran it through a validator first (if I must learn, I wanted to learn solid code). Validated :D Justin seems like a rock solid guy. Was so relieved that the theme was free, that I paid for support, which I used sporadically. Becoming aware that my year's subscription will soon expire, and wordpress is getting into 3.0. I am going to need hand holding. Do I want to pay again?
Discovered Thematic. Still a noob. Everything is free and there is a solid and active community (though I have just registered). Also validates. My child theme is still quite ghastly, and I have done most of the figuring out already. I should be able to port the code (hopefully). So shifted.
So actually, I have shifted (or am in the process of shifting) from Hybrid to Thematic simply because its solid and free. I don't know if its the design or the hierarchy of the community, but I like the feeling of moderators and community rather than one person to answer it all, though Justin is plain awesome in that regard.
If I had to venture a guess, it would be that many people are in my situation. They seem to run hybrid, because their thematic isn't yet ready. Why Hybrid first? It gets found first. I can't figure out SEO for the life of me, so no clue on nuances, but After thesis, Hybrid is the most easily found framework for someone ripe for that kind of thing.