I've been using ERwin for perhaps 8 years, now, and it leaves a lot to be desired. I've been using it less and less as time goes by, especially since SQL Server 2000 introduced the table design editor which works nicely.
Saving preference things (like the object filters) does not appear to work at all. If there's a way to get default behaviors working the way I'd like every time I start up a new model, I've never found it.
The compare feature is just about useless. It's certainly the case that you can create a model in ERwin, forward-engineer it out to your database, do a compare and find that the database and the model are "different." Until recently, I often found it easier to script out databases to flat files and use the "windiff" text comparison utility that comes with Windows than to fiddle with ERwin to see how two databases differed. Late this summer, I finally bought SQL Compare, which is great at database comparison (I can recommend it) but I shouldn't have had to spend the money because ERwin should have been able to do the job for me.
It doesn't seem to support trusted connections.
If you change things in the model and forward-engineer the changes into the databse, the forward-engineer task usually fails.
In spite of years of use, I've never become comfortable with the user-interface.
Its reporting capabilities are a joke.
The auto-layout feature doesn't even attempt to pack tables into a reasonable amount of screen real-estate. Objects end up spread across a very wide model.