Ah...I think (hope) it's nothing to worry about...I have the exact same "problem"! I've had my valve cover gasket replaced a week ago (changed oil and filters and stuff at the same time) and they "spilled" the hell lot of oil when they were removing valve cover and gasket (as I understand it was old oil). It was literally dripping down the exaust manifold...they wouldn't even notice that but I asked them to put a car on a lift when a job was done so we could check for some suspension stuff - that's when I noticed it. Even after they did some degreasing and cleaning I was to choke myself from oil burning residues on my way home...it was smoke all over the place - under the hood, in the cabin etc... Now, after a week or so I can still smell the damn thing from time to time...I can smell it for a split of a second now and then...maybe it's not even there anymore, but I became alergic to this smell that day...I guess I'll be "smelling" it for the rest of my life! lol