To your knowledge did the tune-up involve any adjustments or repacking of the headset, bars, or brifters?

In all likelyhood, yeah, a quick tweak will take care of it. It could be the shop guys cranked too tight on the bearing load. Or, in case of bar or brifter adjustment, one of the screws might be a little loose. Any number of things.

Do you notice any play or knocking in the headset? So, straddle the bike, lockup the front brake and push the bike forward. Does the steering column move at all, independent of the rest of the bike?If so, you're a little loose. On the other hand, if its too tight you'll have a dead spot in the turning radius, where it seems to get stuck. That would be to tight. For safety reasons, I'll say pop over to parktool.com and read through the headset adjustment procedures for your type of headset.

Also, check your cables where they cross the headtube, mine will occasionally slap against the headtube if I'm really working the bike.

Otherwise, check all the bolts and screws and snug them down.