Here is the scoop that I got from the Glock rep:
The 37 is the same size as a 22 or 17, and is chambered for the .45 GLOCK cartridge, which is a .452 caliber bullet in 185 or 200 grains. The case length is shorter than the .45 ACP, in fact, it is the same length as a 9mm(x19). Speer is making the ammo for Glock, and they are showing specs for a 185 grain bullet at 1040 fps and a 200 grain at 984 fps, which is nearly identical to .45 ACP loads, if my memory serves. The basic idea is to put .45 ACP performance into a smaller package that more folks can handle in the fat Glock grip. Glock says that dealers will start seeing them around June 1st. I personally feel that Glock is filling a hole that isn't really there, but I guess that is why they are rich and I am not. Anyway, hope this info helps!