I own and carry a S&W M-60. Typically I carry .357 Remington Golden Sabre 125g JHP rounds. I practice with whatever .38 ammo I can get that is cheap, of decent consistency and pretty accurate. I do this for 4 reasons:
1) Shooting .357 ammo in that thing is not the most pleasant experience. I do shoot my carry load from time to time just to keep used to it.
2) Practice-grade .38 ammo is typically a lot cheaper than .357 ammo, especially my carry load.
3) To save wear and tear on the gun.
4) Most cheap range ammo is reloads, and if you get an over-pressure .357 you can have a real disaster. If you have an over-pressure .38 it will probably still be within the limits of the .357 revolver.
Back when LEOs were carrying S&W M19s or M66s, may of them did this same thing for the same reasons. Of couse, you must shoot your carry load from time to time to stay used to it.
Some of the new .38 ammo (such as the Federal Hydra-Shock) is pretty potent and if you want to carry a .38 load in your revolver they probably perform about as well as the .357 mag. HOWEVER, recoil and muzzle flash are about the same too in my experience. Also, I'm not certain the .38 is rated for +p loads, although I can't imagine it not being since the two guns aren't much different in dimensions.
As far as your second question, recoil is worse than a GP100 or S&W 686, but it isn't really bad. With the right load (such as the Remington mentioned above) it is definitely controllable.
