Three years! One year max for mine and more like 7-8 months. No charcoal versions. Every one I tried restricted the airflow too much. We all do whatever works for us. And yea, you're right. That is nasty. LOL
A fellow member's recent post inspired me to replace my cabin air filter. It's been 5 years and about 100K miles since the last one. I had to take the glove box out because the filter frame is rigid and pushing against the back of the box.
It is dirty all right. Hey the back side looks brand new so let me just flip it over!
... Naw I don't want to give the man a heart attack.
Edit: Put a new one in just now and will see how much difference it makes on my weekend road trip. Silly me, didn't think about the restriction on air flow all these years.