We use it (specifically, Unity, Logging and Validation), and I can't say I'm a big fan of it.
The logging block is definitely over-engineered, and ironically still lacks a lot of flexibility. I was amazed at how much code I had to rip out and replace if I wanted to write more structured logging messages to a DB rather than just a single table with generic messages. The documentation is sketchy, and it's really hard to follow what actually happens in your logger.
Unity actually works ok though. Personally, I'd rather avoid DI containers entirely, but if you have to use one, Unity seems fine.
I haven't really been involved in the code that uses the Validation block, so I can't tell you how that works out.
But in general, I'd say that yes, it is overengineered, and unless it does exactly what you need out of the box, you're probably better off without it.
