I've been using a setup like this for the past year. I use a 4" think filter to reduce strain on the motor though (it's pleated, so a lot more surface area to pull air through than the thinner ones), the idea being reduced strain on the motor. I also stick a carbon pre-filter in front of it.

I get smoke wafting in from outside via window air conditioner - and I think my neighbor occasionally smokes in his room.

I'm planning to setup another to better cover my open floorplan.