Wow, thanks for all your trail anecdotes! It sounds like it's really just luck of the draw, but one thing I've learned is to have a backup plan in case you get mosquitoed out. Maybe I'm a softie, but when there are clouds of mosquitoes everywhere and you can't swim because you'll get eaten alive when you get out and I'm running low on deet ... time to pack out.
I'm starting to enjoy September / October / November trips more and more now because less mosquitoes, though unfortunately that's prime yellow jacket season and I'm allergic. I'd take cold to bugs any day.
My trips for the season were as follows -- with mosquito notes. :)
June 21 2009 Warren Lake. Tons of melting snowfields, very few mosquitoes (??). Trip report
July 5 2009 Dinkey Lakes 3 Sisters loop. Horrible clouds of mosquitoes everywhere, even at 10,000 foot super windy ridges. Never seen it so bad. Trip report
July 21 2009 Emigrant Wilderness: Bell Meadow & Piute Lake. Almost as bad as Dinkey Lakes. Mosquitoes cut our trip short (so we drove to Mono Lake, June Lake, and did some wine tasting in Murphys on the way home!) Trip report
August 14th 2009 Saddlebag Lake to Lower McCabe Lake. Mosquitoes were not an issue at all. Mark seems to have the same experience.
September 23 2009 Cherry Lake to Lord Meadows & down Cherry Creek Canyon. No mosquitoes! But tons and skads of these small little flys that look like fruit flys, are attracted to humans like mosquitoes except don't bite, hang out in shaded woody / damp areas, and constantly fly in your face / mouth / eyes / ears. Mosquito headnet required to preserve sanity. What are these things? The 3 times I've done Cherry Creek Canyon, these things are always waiting at Cherry Lake (but not always so bad in the backcountry).
On the plus side: NO BEARS!