Craig Hockenberry shares some delightfully useful information for developers who need to get out a quick bugfix for their iPhone apps:
An email to appreview@apple.com that explains the critical problem and which product is affected will help speed your update through the system.
Note however that, as he points out, you must not abuse this. Only use it for problems with application review times, and only when it’s an absolute requirement (not a ‘gee, wouldn’t it be nice if my app was reviewed faster’ case).
Remember: with great power comes great responsibility