I've been trying to write an open-source profile provider to work against PostgreSQL (I was frustrated with the limitations and incompleteness in the other projects I'd seen available), but the documentation and examples of how people use it was surprisingly sparse. Even the SO tag for asp.net-profiles has a little over 100 questions associated.
The more I dig in to making it work, the less and less practical it seems; the value added does not seem to justify the complications associated; additionally, it only seems to work on a limited scope of web projects without a bunch of extra work.
I feel like I'm being led to the conclusion that it is not a popular technology, and that there are better ways to persist a more robust user-based information set.
Is my take on this fundamentally flawed? Is this widely used? I'm on the cusp of abandoning my profile provider as it seems to offer little of value.
No, the Profile system in asp.net is not widely used, primarily because of the reasons you mention. It's just not useful for a lot of people.
The easiest solution is to simply create a profile table in your app, then key it on the ProviderUserkey of the Membership system.