As @Jake Wharton himself pointed out this is just not true. Using the existing code and examples, it is a simple and fairly quick implementation for creating custom ABS activities and fragments.
I use library projects extensively, including having library project references that go multiple levels deep. I've run into a few issues, but nothing that was a deal breaker. Eclipse gets confused sometimes on rebuilds, but usually cleaning all the projects gets everything sorted out. Library projects are getting more stable all the time.
This is actually two points, but with a similar theme -- for any library, not just ABS, you have to tradeoff the value you get from including the library's features against the cost of doing so. I feel the value of the interface right now is worth the extra effort and apk size. This is a value decision that needs to be made on a per app basis.
@Ahmad is correct, ABS poses obvious no limitations on 3rd party libraries. It might take some coding to integrate, but they should work together. Furthermore, ABS use will fade naturally in the future. It is a compatibility library, so as the device distribution shifts more and more to Android 3+ devices, the need to support action bar UIs on 2.X devices will be less of an issue.