Are you thinking of this gun for concealed carry? If so, I think one of the main things to consider on this topic is the list of very small guns on the market that shoot 9mm versus the number that shoot .38. I just bought a S&W 642 Airweight (5-shot snub-nose .38 special +P) for pocket carry. I own a Springfield XD-40 Subcompact that is just too thick and heavy for me to comfortably conceal in all situations. The 642 feels like half the weight of the XD and easily slips in a pocket. It seems like the "micro" 9mms on the market are either VERY expensive (Rohrbaugh - $900) or have caught criticism for being slightly less than reliable (Kel-Tec, Kahr, etc.). Of course, I'm sure people who own these pocket autos will chime in to say that their's is always reliable. I digress...
As stated in some above posts, the .38 special has been around for a long time and I'll bet that in the overall history of the U.S., more police officers have been armed with .38 special revolvers than any other firearm. Many still carry one as a back-up, and when I took a trip to Washington D.C. last year, I noticed about 90% of the security gaurds at the museums carried .38 revolvers (some may have been .357, but they mostly looked like S&W .38s). My point is the .38 special has been proven. In most imaginable self-defense situations, a "hot" .38 special +P hollow point is an excellent round. So is the 9mm. They both have their strong points and their weak points, but if price, reliability, and concealment are issues, I would say the .38 special gives you some better options for firearms currently on the market than 9mm.