I use them almost exclusively for bittering: high AA and not at all harsh, pretty much my go-to bittering hop. As for flavour addition, they are very, very mild. I've never been able to pick them out on the beer, even in a single hop stout.
Echo what @jceg316 says, in that they don't return alot of flavour, although from memory what you do get is nice and fruity with a refreshing menthol edge that is quite unique and their most distinct flavour. This was a while ago when they were a relatively new hop, I've not used them in along time.
It's hard to use alot of them in the kettle, due to the ridiculously high alpha acid.