Well, when I get my system installed.. eventually.... some day... soon I hope.. lol I plan on getting a Dwyer gauge put on it so I can see the pressure drop across the filter. Once it gets too high then I'll swap it out.

Granted this is way over kill for most people's houses, but I'm a HVAC guy, it's my duty to overkill my own system a bit with toys. Plus they are cheap on e-bay.