Wow, I'm a big slacker. I check them every other month or so, replace them when they start to show dust/dirt visibly collecting. They may not get quite as bad here because I don't open the house up excessively. My wife's asthma seems to be a little aggravated by Spring pollens, and I tend to be a little more bothered by Fall. Bought a couple of Honeywell air purifiers to help in those seasons.
When I arrived in Spring Hill in 2011, I heard the air return wheezing at the old farmhouse offices of the church one day. Checked it and it looked like a carpet! I changed out 6 filters there that day, not a one you could see light through. So, I guess I'm a slacker, but I ain't low man on the HVAC totem pole, and I've never in my life lost a motor on one of our systems.