consensus seems to be that oil should still be changed at 3 to 4000 miles intervals, no matter what you use. www.volvospeed.com in the FWD section Rich a master tech talks about intervals and having sampling on your oil done.

me i change it at 3000. if you drive about 18k a year slightly more than the national average you only change your oil 6 times versus 3 (plus or minus a little) at most your saving like 100 bucks a year even less if you do it yourself or take it to a fast lube. Yes they suck but are better than nothing.

changing oil and other fluids is probably the single best thing you can do for your car.