my car was serviced, and fine when dropped off. Then about 1-2 miles after I drove it, the check engine light went on. This has happened twice, and they don't seem to know what it is (other than have I checked the gas cap). Anyone know if it's okay to drive until it can be picked up again? It isn't making a big noise or sound.

 

It should be okay to drive until it gets back to the shop. They need to read the fault code to tell what it is.

Just don't take it to be state-inspected for smog if your state does that sort of stuff. They will fail it.

 

I agree with Lugnut. Plus many repair shops, and some Auto Parts stores (AutoZone where I live) will read the problem code for free. I guess they do this is in the hopes you will have it repaired by them or buy replacement parts from them.
Your situation is similar to mine. I just had a major service done on my C280, and now I have a CEL and a blinking fuel guage light. I went to AutoZone and found out it was PO455 (large EVAP leak). 90% or the time-or so I'm told- this is a gas cap issue. Well, not in my case, however, knowing the code, I know it will do no mechanicel harm to drive, but I simply would not pass an emmissions test.