I started using seam one week ago.
In the beginning I was surprised about how easy it might be for creating application. But after a while I got frustrated since it didn't work like given in the manual. I followed step by step the instruction, but unfortunately I encountered several problems.
The recent thing I did was using the reverse engineering tool for generating entities and the uis. Afterwards I had to manually delete about 70 % of the classes since they contained dots. Since it is a Java policy not to use dots in class names the compiler complained a lot (over 6,000 errors). So, if anybody knows how to avoid or maybe configure that, I'd be curious.

The few remaining entity classes and uis were also not working. I got several exceptions. Unfortunately, it is not very clear what is exactly the problem. The stack trace is huge but it always consumes a lot of time to determine the actual problem.

Last, but not least, it's a pity that it is not possible to have more then one project open at the same time. Currently I have three seam projects. Unfortunately, I have to reenter all configurations again, when I want to use seam restart or the other options.