I'm looking at the Polaris 800 v. the Yamaha 700.  Sportsman v. Grizzly.  I will be using it to tow a trailer up and down hills (total weight about 650 lbs).  Both machines appear good.  I've read about quality issues with the Polaris, how about the Yamaha?

Any thoughts?

RTR  

Yamaha machines have very few problems.
if you check out the consumer product safety commissions website, http://www.atvsafety.gov/atvrecalls.html

you can see that Yamaha for the past ten years or more, has only had 4 recalls and none of them current.

while Polaris has had 16 recalls including current recalls for their 2008 line.
most of the recalls are seriously dangerous to the rider, and injuries were reported.
a good number of these recalls have occurred in numerous models and occured in different year models, including the new models.

the Yamaha, pound for pound will last you longer, cost you less, and be less dangerous to operate than a polaris atv would be.

when you consider that Polaris has had to issue recalls for the steering stem breaking on their machines while riding, and the brake calipers falling off while riding, fuel leaks that cause injury due to fire hazard.
fire hazard recalls for bad cdi boxes.(one guy on here had his house catch fire and burn half of it and his new car due to his polaris catching fire.)
and reports of the transmission bolts backing out causing the transmission to lock up while riding.
these are seriously dangerous recalls.

the choice is yours, but if you buy a polaris, park it outside of your home, and not close to anything that will burn, and be ready to pay out of your own pocket for repairs because the polaris dealers have a nasty habit of not honoring the warranty.
and ride very slowly while wearing flame retardant clothing.