I've owned a 98 Magnum 425 4X4, which my son now has, and an 02 Sportsman 400 that the wife now rides. Never had a major problem with either one and they've been great bikes. We use them all year long around here too, to work with and repair fence etc!!
The ONLY thing about a Polaris ATV, 500cc and under is ALTITUDE. If you go hunting like I do in higher altitudes in the fall, you need to change out the jet and adjust the air intake. I live at 989 ft elevation and I hunt at about 10500 elevation. Polaris ATVs are very sensitive to altitude changes that drastic.
Otherwise, I think Polaris is a fine ATV, IF you like their EBS, in the bigger cc bikes!! I think it's a little radical, so I ride a Bombardier Quest 650, and love it!!
For more info, you could come over and join us at ATVFrontier.com for discussions on all makes of ATVs in general.