We've used a local PR firm for our UK e-learning business (tuitionkit.com). We got a few newspots in local papers and the like, but nothing too groundbreaking that put us on the map. I'm not entirely sure it's the perfect fit for us.
The key point about engaging PR folks is that the longer you give them in advance of launch the better. We contacted them about 2 months before we launched (we launched back in April, so it was February time) and they said they like at least a 6 month run up to do the best job they can.
