I've never had a problem using a valet, and don't think twice about using them.

Incidentally, I worked as a valet parker in my teens, many years ago.

It is about judging the competency and professionalism of the person parking your car, not whether or not you use a valet, IMO. Whether you or the valet parks it, it is more likely to be hit by the car beside you (since there are two of them being parked, and just one of you). You need to decide if the valet is more likely to be careful than the other patrons of the establishment who would be parking themselves, especially if they come out after having had a few drinks.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue