I've had mine since last summer or so. I have the P229 9mm conversion bbl. For me it was a drop in. It has worked 100% and I have actually stopped using the .40 bbl. I enjoy the 9mm in the p229 better. I never warmed up to the .40. It was fun to shoot, but I wasn't consistent with it. Putting the 9mm bbl in the gun, it has become one of the pistols that I shoot the best. POI is a bit different than the .40, but not too far off, no need to change sights or anything.
Do NOT be in a hurry for the bbl to arrive. I had to wait over 2 months for it to ship (ordered 3/7/05 arrived around 5/26/05) If it's not in stock, you'll have to wait for a production run, which was my case.
It was a great purchase for me though. I liked the sig, but it wasn't one of my favorites until the bar-sto. The .40 mags have worked great with the 9mm rounds. I can fit 12-13 in the 10 rounders and 14-15 in the 12 rounders. I have not had any failures of any kind with the bar-sto, but I have only run WWB value packs through it (no hollow points)