some people have had balancing issues, some haven't.
the 'people' you've heard saying that they wish they'd gone with the stock OR size are usually: MC, someone else, MC, MC, MC, someone else...you get the picture. i understand why he says it, and very valid reasons (better gas mileage is a big one). he just says it alot.
you'll lose some ride quality, as you'll probably go with a LT tire vs a p-metric tire, but (for me) handling characteristics are night and day from the stock rugged trails. better wet/dry traction, handles turns better etc. Rugged Trails suck.
I have had no balancing issues at all. infact i'm overdue for a regular balance/alignment checkup, but haven't noticed any adverse effects. saying that, there are a large number of people who have had some issues. BFG states that you 'should' have a 7.5" wide rim (stock rims are 7") and you might even find some tire vendors won't put the tires on your stock rims for this reason.
as for gas mileage, went from 19/22 to around 17/20 with the tires. i might've gotten less of a drop if i'd stayed with 265/75R16, but i don't believe it would've been much.
I've had good luck with mine i guess... no balancing issues, no warranty issues(dealer replaced a front shock for me...after the lift), not that big of a gas mileage change. i had a bigger mileage change after the lift.