Office 2004 was never UB, and that's one of the reasons that I decided to get the new version.
Is it worth the hassle? Well, some people seem to like it, but it's gotten a lot of negative feedback (particularly because they dropped VB support). Of course, if you've never used VB, then this probably doesn't affect you in the slightest.
My use probably isn't typical, but the biggest problems I've been having have to do with document sharing. If you need to send documents out for other people to work on, chances are they're using an earlier version, and so you'll spend lots of time working on .doc, .xls, etc, files in "compatibility mode", since the new versions all prefer their native .docx, .xlsx, etc., formats. (Although you can save, for example, a .docx file as a .doc file, and so forth.) This sort of defeats the purpose of having the new edition, since it doesn't seem all that much faster, and I'm still working in the (now) legacy formats.
Other than that, I've run into lots of other problems. See
this one, for example, or go to the Word user forum at that same site and search for "Equation Editor".
I still need to work with Office files, but I spend a lot of time transferring things back to my old PB (with Office X) to fix things.
I was happy with my older version of iWork, but I got so frustrated with Office 2008 that I decided to get the new iWork too. No complaints there, and it's about 1 GB smaller than the previous version!