I used to work at what I like to think is the coolest independently owned Mac specific store in Allston, MA. It’s called the Computer Loft and it's like walking into someone’s very cool playroom that happens to be packed with new and used Macs, guys fixing Macs and eating, drinking (non-alcoholic beverages, or course, and occasionally smoking).
Not sure if the boss is as lenient now as he was then, but the general rule was as long as you got your work done, MULTI-TASKED, and didn't frighten the customers, you were cool.
Anyway, when taking Macs in for repair, I came across some of the most heinous cases of dust collections imaginable. My boss would get pissed if we used air cans to clean them and rightly so - those cans are expensive - so what we used to do was take the offending Mac outside (who wants all that crap inside?) and use an industrial strength vacuum cleaner with a hose-like attachment to suck up as much off the gunk as possible. Once most was gone, we'd reverse the direction to blow air and, being careful not to blow any dust INSIDE components as Mark points out, get the remaining dust out.
Does this help? Not sure, but it was fun reminiscing.
Seriously though, if you use canned air, also be careful when spraying close to chips and mobo parts as once in a while the cans will blow freezing air instead of the normal cool air you expect. This can hurt fragile chips.
Now go clean that monster.