I have used it on a couple of medium-sized projects.
It has quite a few bugs in the current release that are a pain. If you plan to evalute it, I recommend waiting for version 1.1 which is supposed to be out this month.
Model-View-Presenter is optional in the WCSF and mainly used for testability of the UI. It also does abstract your application from the view, so you could use it with other projects but also with different views in the same project. The WCSF Team doesn't push the MVP Recipes, just provides them for you if your project needs it. If you do need MVP, the recipes are a huge productivity savings.
The WCSF also has Dependency-Injection, Service Registration and Location, Page Flow, and other nice features. The Page Flow Application Block is really sweet when you have complex page flows and you want to have the ability to maintain them separately using WF. So, it is more than MVP and there are some nice features.
If your application could benefit from such features and you aren't up on all the technology, the WCSF is a nice starting point.
If your application doesn't need the features, it is overkill.
If you are already familar with the features and have your own solutions to these challenges, you may find the WCSF a bit less functional it its 1.0 version.
For smaller applications or applications that are primarily CRUD database applications with little business logic and little need for flexibility and extensibility, this is not the answer.
WCSF 2.0 is expected to have more Rails-like features, but that won't happen until closer to end of the year.
Regards,
Dave