I recently had a 100,000 major service on my 2004 TL. Within a couple days I noticed a pronounced smell of burning oil. I have since noticed a puddle of oil has formed under the car and just today there was light smoke coming from under the hood after driving a short distance. I have an appointment with the service center in two days, but is the car safe to drive in this condition?

A leak of some fluid, probably oil, dripping onto the exhaust. This smells terrible, and it only needs a drop or two.

Check your valve cover gaskets, bet they are leaking and that is burning off.

Does the engine burn excessive amounts of oil? That may be the cause of the smell

Good guess. It's not hard to access the switch on your car. Follow the steps at the link below. Remove the switch and inspect for heat damage. If there is no obvious damage, test the switch with an ohmmeter. Jiggle the switch while testing.
Repair Guides Steering Ignition Switch AutoZone com

Its either leaking or burning it---look for any signs of oil in the cooling system or water in the oil---could be a gasket going bad somewhere.

if a leak it has to with that much oil loss show somewhere.

I would if you cannot locate it act quickly and have a mechanic look at it before it becomes major or fatal issue.

I hope you changed the oil again to take there oil out, could be wrong oil, and ruin engine for sure. Oil in cars today mean alot. Try that but let me know, thanks, Frank

I was recently changed the cabin filter on my TL 04, i don't think it necessary, it is more like optional but if you change filter for your engine, why not change the air you breathe inside the car. After i change my cabin filter i noticed more air are been circulate through out and also fresher than before. the price for a cabin fiter is also relatively cheap less than $10. took me 15 mins to do it. check it out at http://www.youtube.com/watch?v=FQsDxqxyeqM

Smoke from that area is likely steam. It's possible that you have some slight seepage from the radiator or one of the hoses up front. At this point, the coolant loss is very slight and you may not see much in the way of dripping but there may be a wet spot on or near whatever is leaking that you can locate after it's been run and shut down for about a half hour.
You can also have a shop do a fluorescent
dye test to locate the problem.
Catching any leak while it's this small can avoid major problems later, so don't ignore it...leaks don't get better, they get worse.

I've noticed lately that many people are reading many of the answers given here and not bothering to note if they were helpful. don't neglect to do that as well!!!!
Good luck

Intake manilfold gaskets, valve cover gaskets, oil pan gaskets, oil sender,

hi tina
it might be a few things unfortunatly, 77k is not much for these cars but allot can go wrong with them, i can start with, valve guid seals these tend to wear arround 100,000 but deppends on use, wether hard driving or town, so you could be getting close to these, you can also check visually if there is another leak from the valve cover on the rear side or this might just be ressidue from the previouse leak, sometimes the smell of unburnt fuel can fill the car if the wind is blowing in opposite direction when standing still can fill the cab with fumes dont worry only minor, it possibly is the cold air rather than smoke condensation from the exhaust is warm and hitting cold air will do that, it dosent realy sound drastic and just keep an eye on the fluid levels as you are doing but i dont think there is much to be concerned about....hope this helps