XP makes loads of restore points.
Vista makes fairly regular Checkpoint restore points.
Win 7 seems to get around to making one eventually.
I manually create one prior to installing something new and Revo creates one every time I uninstall something. When in doubt,make a new one.
You can assign a percentage of your drive space for use as restore points (Vista default was 15%, which with a 1 TB drive is a lot) Once this capacity is exceeded, it overwrites the oldest ones first.
Increasing/decreasing the amount only gives you more or less available points to choose from, it will not change the amount of points created.
Full image back-ups are great, but if a system restore will fix things, using one is overkill.
BTW, CCleaner Tools section has a restore point removal function, handy for dumping the restore points you don't want or need to keep. I usually keep 3-5 of the latest ones.