doesnt it say every 50k on it, in normal conditions? i was told that the k&N filters better if has some dirt on it. idk, maybe not. lol
from k&n's site
20. How do I know when to clean the filter?
The general rule of thumb is that the filter needs to be cleaned when the dirt build up gets as thick as the wire mesh. The usual interval is 30,000 - 50,000 miles depending on driving conditions. We recommend that you check your filter about once a year in normal usage.
the more you clean it the more oil and crap gets on your MAF, IAC and will cause other problems. but this is a known problem with filters of this style anyway.