Sounds like a great book!
I'd say we have a few challenges so far that we're working though. We like the process, generally, but still have a few stumbling points.
Tools are always an issue with anything I guess, but finding something that will work company/department wide has been a bit of an issue. We went head first into Hansoft and are still trying to bend it to our will. When you're trying to adapt both new processes and new software it gets to be a little complicated.
We're still trying to find the best task size for developers for our 2 weeks sprints. I'm the Scrum master (which I'm loving) and also the QA resource on our team, so I'm usually pressuring devs into making their dev chunks small enough that I have stuff to do QA wise throughout the two weeks, inetead of all piled up on the end.
Our other big issue is defect management, which I think is also a tool issue. We went from Microsoft Test Manager and TFS, which had some pretty strong bug recording features, but the version we had was weak on the reporting side. We're trying to get Hansoft to do the job for us as much as possible, but I haven't really been loving it yet.
To add to the fun, our QA department recently moved away from traditional test management into Session based test management. Another curve ball which is, overally, a good shift, but another challenge to make it all work together. If you're not familliar with SBTM, check out a guy named James Bach's work. If you don't drink his Koolaid that's fine, but I think he make some good points about how testing should be done.