1997 Mazda 626 LX w/smoking tail pipe! Please help!

I have a 1997 Mazda 626 with approx. 160,700 mi. I've just had an extensive tune-up performed - including spark plug wires, spark plugs, pcv valve, and valve cover gasket all replaced and an oil change. The next day after recieving my car back, I noticed that after a cold start, white smoke is emitted from the tail pipe for 10-15 seconds. Once I get on the highway it usually blows out completely before I reach a destination. The smoke has a weird scent. The mechanic told me many cars emit a bit of smoke after a cold start but this is not normal as my car has never smoked from the tail pipe before.

How serious could this problem be and when do you recommend I have it checked and repaired?

Thanks a million