Most Technical Writers have had experience using FrameMaker as the backbone of their writing shops and find it a little cumbersome. However after a little ramping up, most get used to it and often uncover some very cool features that you can use when you have to manage large volumes of multiple documents with single source content and chapter and book modularity. FrameMaker integrates pretty well with other Adobe products (and it should!). You can also easily generate decent web output with it's integration with WebWorks Automap and ePublisher.
Room for Improvement:
One thing that bugs me about FrameMaker is that when you are dealing with large files, it sometimes hangs and can seize up your local PC or VM resources. Make sure you have a beefy machine running the app if you plan on generating and working with files over several MBs.
FrameMaker also has a scripting component that works pretty well and you can automate the update of books and generation of output very easily. You can have jobs running in the background while doing other tasks and set off "builds" after hours to save on resources.