I have always had great results with all rebate programs. The only exception being a memory rebate from Tiger Direct.
I have personally sent in 2 OCZ rebates and they have both come back (one did take awhile but it arrived none the less). My friends have also had great experiences with OCZ, between them all they are 5 for 5 with rebates. Also their tech support has been awesome, they responded quickly and efficiently and they helped us locate the problem (which turned out to not be their fault at all). I have also heard of people buying 4 sticks only to find out that their motherboard wont run all 4 modules at full speed, so OCZ allowed them to trade them in for 2 modules with the same total size.
In my personal experience almost every time there has been a problem the error was PEBKAC (myself included in the one time I had to call up OCZ).