Thanks for your answer!

Well I should probably remove the "smell gasoline" mention. I noticed that only once, and when I tried tonight I could not smell anything. I have also carefully inspected my car's parking place and I did not find any trace of gasoline.

But the starting problem has been going on for the last 2 weeks and can consistently be reproduced. It is almost looking like:
- engine cold: start OK
- engine warm: hard to start
- engine hot: start OK

I am going to take the car to the dealer, but unfortunately they are fully booked until Thursday. So I have to leave with this problem until then (unless I find a way to fix it myself).

I have been thinking about changing the plugs, but after reflexion I do not think they are the problem. If they were the car would be hard to start every time.

BTW if you know a good mechanic in the bay area, I would be very happy to show him the car.

Sylphe