Right now it's impossible to tell which version of Thrift you have installed. If you're depending on features that have recently been added (and that subtly don't exist), you can spend a lot of time chasing your tail trying to figure out what the problem is.
This may be something that has to be implemented piecemeal on each client library (ruby gem, java classes, etc). Thoughts?
While we're at it, let's add a --version switch or something to the compiler so you know what version of stuff you're actually generating.