As I'm in the same boat, I can definitely say that you CAN do pretty much everything you would want to do in FileMaker. Such as hosting user connections... Instant Web Publishing, etc. I'm slowly grasping the database concept, and if you already have the experience with database design/programming I don't see why you wouldn't be able to utilize the software.
The nice thing I have found out about FileMaker is the ability to scrap your T.O. relationships and visually start over. I've used the relationship section in manage database as a whiteboard quite a few times... But i'm just a novice when it comes to databases & ERDs.
I'm sure that with a proper education on database design & theory you can quite effectively utilize this software, but you could also utilize any other database technologies and achieve something similar if not better. I wouldn't consider FileMaker to be the "end all, be all" solution to database design... but if you want to get your feet wet, it's not something you are going to mess up easily.
FileMaker has a lot of UI quirks, so if you MUST use the software be aware there are limitations on what you can do and how you can do things.