I work in an auto shop and I have to tell you if you dont recommend a specific type of oil to be put in your car, a lot of places especially the one I work at, will pour anything down your engine.
Also watch to see them doing the oil change, watch what they put into your engine.
The shop I work at here in california is Goodyear and these damn poeple will not order 10-30.
They just tell me to go ahead and use whatever is on the shelf.
Every oil change Ive done has been used 15-40 or 20-50 on mostly 4 and 6 cylinder cars.
Just some engine damage waiting to happen.
I dont argue with them i just do my job, but ill never take my car to a shop to get my oil changed, ill do it myself, plus you save a few bucks.
Guys if you got the know how, work on you own Caddi's.
Later

Agreed. My wife works in insurance, and you wouldn't believe the claims that come through from oil changes places for improperly installed drain plugs, overfilled crankcases, gear lube in the engine, or engine oil in the transmission.

I've done my own changes for 25 years. At least I know who to bitch at if something's not right.

Yeah there was a guy that graduated from my high school a year earlier who brought in his '86 Monte Carlo SS to a Jiffy Lube to have them change his oil, and they drained it, but never put any oil back in! So about a mile down the road, his engine seized and they found out what they did and basically gave him money for that car, and he went out and got a '96 Riviera with the supercharged 3800!

Just proof that if you dont know whats being done to your car or dont know whats going on with your car, its just damage waiting to happen.
Later

I never had a problem with engine oil but it seems that most shops are awful tight when it comes to grease on the front end. I have replaced more van front ends in the past 2 years than ever (they have 15 fittings) I agree do it yourself. If nothing else I I save something like $780 a year by doing all the oil changes myself and I save on wear parts replacement.