I've been watching Drupal 7 for almost two years now and have been champing at the bit to start using it. I launched the promotional site for "Drupal 7: Visual QuickStart Guide" in Drupal 7 -- how could I not? -- about a month before Drupal 7's official release. Now I've also taken the opportunity to combine tomgeller.com and gellerguides.com (my portfolio site) into one. The new one is at tomgeller.com, of course; for the moment you can still see the old version (with comments closed) at http://temp.tgeller.com.
The upgrade itself wasn't so bad, although I ran into more error messages than I expected. But merging the two sites was frankly harder than I expected. There are basically three options for transporting nodes:
I mention these options -- and a lot more -- in the paper I wrote for Acquia, "Migrating a Web Site to Drupal". (That link takes you to one of my Panels- and Quick Tabs-based portfolio pages, which I'm very proud of.)
Beyond node migration, there were other surprises. For example, messages that Drupal automatically sends to users -- to confirm their membership, for example -- use old-style tokens like !username instead of [user:name], and have to be changed manually. I missed a theming change that threw some baffling errors, and had to drop some functionality because the modules weren't ready. Then the statistics table stubbornly refused to update properly -- until I moved the site to its host.
So what's the prognosis? I agree with TimOnWeb.com that your situation dictates whether to upgrade to (or build anew on) Drupal 7. The "7.0" label is psychologically powerful, and I made the mistake of believing that its "release" meant that major problems had all disappeared. They haven't; there's still a lot of work to be done. (Speaking of which, please continue to support developers who are working on 7.x projects!)
Having said all that: The proof is in the pudding. tomgeller.com is up and running on Drupal 7, with a hell of a lot of functionality I'd been withholding while on Drupal 6. Enjoy this forward-looking time for all its worth.