For what it's worth, there have been multiple threads on this topic before with more detail, so doing a search will get you more information.
Be careful of lube/grease with petroleum ingredients since that may damage some O-rings. Some products list ingredients on the label but to be sure you should look for an MSDS (material safety data sheet, iirc). For example, the MSDS for the Radio Shack Lube Gel does have some petroleum products in it.
So, if it matters enough to you, you should find out from the manufacturer what type of O-ring you have, find the acceptable type of lube, and then check to see what's really in the lube/grease. Will the O-rings fail instantly? Nah, but they can degrade over a few months or even weeks, and can get into a pretty nasty condition. Much more important to worry about O-rings where your life is at stake (diving, medical, etc. equipment) or where it can cost serious money (engine parts, machinary, etc.), but it is always nice to avoid a headache before you get one.