I use the oil life monitor. It's been proven through oil analysis to be a conservative calculator of when to change your oil. New closed loop fuel injected engines do not contaminate the oil like the engines of the past. Oil forumulations are much improved. Group III base stocks (hydrocracked, highly refined) nearly mimic synthetic base stocks. Additive packages have been greatly improved. Lastly, synthetic oils are absolutely up to the task of completing their life cycle that the GM oil life monitor calculates. You can see a basic writeup of how the system calculates here:
http://www.gmgoodwrench.com/_res/pdf/OLS1.pdf
A search of the internet will show you where the monitor's algorithm is conservative. If nothing else, for your peace of mind, run a good synthetic.
I'm not going to get preachy here, but anything I can do to keep from pouring money to people that hate us, I do. I don't buy chicom crap unless there's no alternative and I have to have it. My spending has gone way down since I started this. Another thing is that I drive a little slower most of the time. I've been amazed at the increased mileage of all my vehicles since I've started this. And I run Royal Purple in everything that rotates (there's other quality synthetics, pick your favorite) and Mobil 1 oil filters.
Seriously, with today's closer tolerances, better filtration, and seriously decreased contamination, it's overkill to do a 3k oil change unless you're racing or towing, but even then, they GM oil life monitor takes this into effect. Oil analysis has shown the system to be an accurate indicator, even conservatively, of your oil life. It will save you money. It protects your engine. Most importantly, it cuts back on how much oil we need. It's really hard to get off of the recreational oil change bandwagon, but it's the prudent thing to do.
If the oil monitoring system were a bad one, you'd be reading all over the internet of engine failures and GM would kill that program yesterday.
Help us save millions of gallons of oil folks, trust the technology. I'm saying this as a certified tribologist and have read plenty on it.