Depends on how you drive (and where--track, autox, street, canyon carving, mixed use, etc.) and how much negative camber we're talking about. Stock alignment maxes out at -1.0 IIRC; another half to one to even 2 degrees may not be "excessive" as the answer is "it depends". Run in an autox will stock camber and you'll eat the outside of your tires very quickly....run an autox appropriate camber on the street and you'll eat the inside of your tires.
The other thing to consider is toe. Toe is often more of an issue in tire wear than camber when camber is a more moderate levels (e.g. aggressive street). Combine toe with camber and tires can disappear quickly. A lot of guys who run a lot of camber tend to run close to zero toe in (or a very slight amount of toe in).
Like anything suspension and tire related, it all gets very complicated very quickly. There's balance between front and rear alignment settings to consider... The type of tire you run has an impact on camber selection, tire pressure makes a difference, driving style makes a difference, and the car and it's suspension geometry, weight balance, etc. play in as well. Skill and ability (understeer at limit vs. neutral vs. oversteer) as a driver play in too. Weather conditions (snow, rain) play into decision making as well.
Stock settings and OEM recommended tires are generally designed for a good compromise between tire life, performance, and safety. These settings will not, however, satisfy more performance oriented drivers--hence things like camber plates, wider wheels/tires, coilovers, etc, and some experimentation and adjusting.
Probably as general rule if you spend a lot of time on the freeway or long distance straight driving you probably want less negative camber; if you drive aggressively on the curves then you probabably want more negative camber. And it pays to keep an eye on tire wear so you can address any uneven wear issues before the tires are gone....
I'd run some searches and see what folks have found works best for various applications and situations. There really is no one "right" answer....
Last edited by Finnegan; 10-12-2010 at 02:05 PM.