On a test server I converted the data from my current b2-based blog to WordPress with very little trouble. Especially helpful was the handy upgrade script included with WordPress.
For the most part everything seems to be working well. I was even able to get the search-engine-friendly URLs working. I may in fact upgrade my live b2 blog with the new WordPress code. However, I want to run a few tests and see if any bugs pop-up before I take the plunge.
One downside is that I was hoping the initial release would include the Smarty Template Engine like the other b2-derivative b2++. However, I see that Smarty integration is in the works, which is great!
So, perhaps I’ll wait until that happens before I upgrade. Probably not; I’m too impatient ;-)