I had mine on for almost 50K miles before I replaced it with a stock Toyota filter for the winter. I really didn't notice much of a performance difference between the two, except the K&N was slightly louder. I took out the K&N because it was cheaper for me to use a new Toyota filter I had in my closet instead of buying another cleaning kit for the K&N.
There are pros and cons of using a K&N filter, and neither one outweighs the other enough to make a difference.
I'll let you know how I feel about the k&N filter soon as it comes in. Placed an order with Brandsport so it'll take a few days. Also ordered the TRD thermostat for the 1azfe engine which will take about 12 weeks according to Brandsport to arrive. Man, that's a long wait.