I've had mine in for nearly 2yrs. Last weekend I pulled it out and it looked just like I put it in new, no kidding. So I just put it back in. Car doesn't sit garaged all year - I actually drive it every so often but I don't have a lot of dusty drives. My approach has been to clean/re-oil based primarily on visual inspection.
Follow Ups
How Often to Clean/Re-oil JWT Cone filter? - darkmann11:43:41 06/19/11