Having never used/heard of credit monitoring services, how are they any different from regularly checking your credit card statement?
They check to see if someone has opened a NEW credit card, or any other form of credit, in your name... You wouldn't even know until you went and applied for a mortgage only to find your credit score trashed! Then you need to file for identity theft etc...
Same goes for credit monitoring, they only let you know, but they'll let you know earlier.
Personally, I'd rather go with freezing my credit so nobody can open anything in my name, I can easily unfreeze it when getting a mortgage :)