I bought a set and installed them about 6 weeks ago. I would have to say that I'm quite happy with them. I feel like I may have lost a LITTLE hp in comparison to the 370's that came out, but they are MUCH cleaner and smoother. The engine is quieter at idle, smokes less, and the engine just generally seems to be much happier.
They did improve fuel mileage a bit, but I can't give you real numbers as I only ran about 1/2 a tank of fuel before making some other changes. What I can say is that I can usually bank on 140 miles to the first quarter tank, but with the new injectors I went about 160.
I have since installed a 100 plate and 4k GSK and am still having fun with the new power and haven't run a good, full tank of fuel through it yet. I am heading over the mountain to Denver in about a week though and should be able to give real fuel mileage numbers then.