RegMon for live monitoring of registry, but a lot of apps are now hunting for traps in the api. I haven't seen anyone check for reg notify routines, but that doesn't mean they won't in the future.

Personally, I've had REALLY good luck with RegShot. It takes a very fast snapshot of the entire registry (and file directories). Then, install your software, and take another snapshot. Hit the Compare button, and it points out what changed. WAY COOL.

A lot of apps will read and write TONs of stuff just to hide what they are really doing. RegShot makes short work of finding out what really happened.

Hope this helps.