Actually, I'm mostly clueless, but I had several good conversations with the guys at Downey off-road on the technical details.
My stock tires (205 / 75 R 14) are 26.1" tall. A 30 x 9.50" tire (R15) is 29.5" tall and requires more power to push down the road - about 13% more - which can be achieved by changing to a "lower" ring and pinion gear size (actually a higher number e.g. from 3.56 to 4.11)
If you went with a smaller tire diameter, the performance hit would be less and you could get away w/o the gearing change. Alternatively, if you don't mind losing some power (and with only 112 hp on the 22RE I sure would be) you can skip the gears and fix your speedometer with a Truspeed recalibrator.
The bottom line though is what are you trying to accomplish? Believe me, I would SO go for 33" tires and an LSD on my truck to go play in the dirt. But those tires won't fit unless I either install a body lift (a whole new set of problems) or rip off the front fenders and the sidewalls of the bed!
While it's certainly possible to make a great desert rat out of a 2WD yota, the "barrier to entry" - meaning what it would cost to get what you (or at least me from my point of view) really want is just too high, IMHO.