I just tried it today too. I exported all of my feeds from Thunderbird and imported them into Google Reader. I like many aspects about the interface and I love the fact that I can access my news feeds from any computer, however, I definitely prefer Thunderbird.
I really like the email style navigation in Thunderbird, especially getting the preview from the website without having to launch another window.
Another problem I had with Google Reader was that it didn't update the feeds correctly. I expected them to be updated realtime (at least when I clicked the Refresh button), but they didn't seem to be. I could view many ch 9 posts in Thunderbird that weren't available in Google Reader. I looked for an explanation for this and never found one.