I have two dozen IP cameras around our compound. Three months after I installed the system I saved myself over $5,000 dollars after one incident.
On weekends, we train dogs at our property. People come from all over the area to train with us. I don't know everyone who trains with us that well, although everyone fills out a waiver with contact information. On one occasion, one of our guests did a significant amount of property damage while backing up with their truck, damaging a gate and controller. I found the damage after everyone had left for the day. Of course nobody fessed up. I pulled up the camera footage for the day and found the 'friend' who did the damage. I told him that he is either going to call his insurance company, or I would call the police. The situation worked out well. I got a check from his insurance company and had the damage repaired. Without the camera system, I would have been SOL.
FWIW here are a few things that I have learned as I set up my own systems:
Avoid wireless systems. They are unreliable over the long haul, even for short distances.
Put multiple cameras on 'hot spots' using different angles.
Always have a camera that can take a good face shot in addition to cameras positioned for 'overview' images.
If you rely on motion sensor to trigger recording, error on the side of higher sensitivity. Hard drive space is cheap.
Test your system. Verify that it is recording as needed.
Review footage from an entire 24 hour period. Make sure cameras aren't facing directly into the sun at dusk/dawn.
A great piece of software to tie feeds from multiple IP vendor's cameras together is
http://blueirissoftware.com/8.html. It's inexpensive and awesome, IMO. No affiliation, just satisfied customer.