Not everyone is thrilled. If you're lucky (as I was with most of my blogs) you'll be able to upgrade with Simple Scripts and everything goes okay. But sometimes Simple Scripts is a bit simple, if you know what I mean. You can find out more here and here. Basically, I found that Simple Scripts is not as flexible as Fantastico when it comes to WordPress configuration. If you install WordPress in its own subdirectory, for example, you may have problems. And Bluehost support doesn't want to know... they haven't a clue what to do either.
To be fair, this appears to be more a problem for us previously existing users rather than people just signing up and installing WP for the first time. But I was a new user once, and I would probably not have chosen Bluehost if I'd known I would wind up in this spot. So buyer beware.