Cirrus,
I originally did an FAA IR just for the fun (and the fact that I did'nt feel comfortable in poor weather although I had an IMC rating) when I was out in the states doing some hour building. A few years later I went onto use the fact that I had the rating to do a conversion to a JAA IR, I passed in 19 hours (including test) this saved me from having to buy the full 55 hour course.
The one thing I would advise is to pick a good school there are many that will get you through the test (with a friendly examiner) but your ticket won't be worth the paper it's written on. Once your done make sure you shoot loads of ils's (as there free!!!) and ndb approachs and keep your own standard high.
have fun
Red