I replaced the cabin air filter in my '08 Subaru Forester X last night. It had been in 12 months and the car sees mostly city driving. The old filter is a TYC 800075P (about $10 on rockauto) and the new one is the DENSO ($19.63). I kind of figured I was replacing it early, but from the looks of the old one I'm glad I did the job at 12 months. I might even start doing it a little more frequently.
TYC 800075P
DENSO FTF 453-5019
Comparison
TYC 800075P
DENSO FTF 453-5019
Comparison