For me, it's fun to THINK like a criminal. Let's be honest, we've all thought "If I'd rob a bank, this is the way I'd do it..."
Most criminals are idiots. And most of the crimes are happen are smash-and-grab, crackhead type petty thefts that these cameras would protect against.
But my thoughts are, what if a SMART criminal were to do this... what would i do in this case?
The lock box idea given by the user above is a good idea, but if I were to see a lock box with a DVR inside... EVEN WITH a tamper switch, I'd simply pour water down the ventilation holes till I heard some crackles and a pop.... and I would continue with my crime spree....
My idea is to create some sort of box-inside-a-box system where if someone were to pour water down, it would flow AROUND the dvr and go through a side channel and come out the other side, leaving the DVR unharmed.
Also, They sell SUPER CHEAP water detection systems (for basements and water heaters), that run on 9V batteries that pretty much last forever... if you stick one of them inside the box, it would go off if someone pours water down it, and that would be enough to scare the thief away before he manages to get enough water inside to harm the DVR.