I was just reading a owner summery on the Prius after 30K miles and noted the following:

Are their filters in the HVAC system that require replacement at regular maintenance intervals?

 

I reached 30k miles in my 04 when it was 1 year old last summer. Since I do my own oil changes, I changed the two air filters myself as well. The cabin air filter (it's behind the glovebox) was indeed very dirty (bugs, leaves, ...) and deserved renewal. This is the first car I've seen with a cabin air filter and from all the junk it collects, I'm glad it's there.

JeffD

 

A cabin air filter in a car is no different than air filters on a home central heating and air system or one in a place of business. Many higher end vehicles have had this feature for years and now it is being pushed down to more common vehicles.

I'm really glad to have it. I believe the dust inside my vehicle is much less than it would have been if the filter were not there. And changing the filter every 30k or so is nothing when compared to the other filter changes on the engine that need to occure more often.