Keads has a good post up on his experiences using various lasers for dry-fire practice. I've been a big advocate ever since I got my first set of CTC grips on a J-frame back in '03 or so; I largely credit them with teaching me how to pull a double-action trigger and actually hit what I'm aiming at.
On a related note: That LaserLyte wall target looks awesome. Do want. (Especially since they don't make a SIRT for the M&P yet, which gives me a sad.)