Its been stated with a lot of testing that most likely you won't see any improvement in fuel economy or even power with a K&N drop in. Basic rule of thumb is that the more airflow that goes in, the more particles get in as well. Decent paper filters and oiled K&N filters do about the same job in keeping your car running. The gimmicky shows they have with KN filters having so much more airflow is usually due to it not being oiled enough or oiled at all. There might be a minuscule improvement, but its certainly not something you'll notice.
I have a K&N drop in mostly because I got the recharge kit for free from a friend, so I figured I'll just use it just so I keep recycling it. I haven't noticed any change myself and really didn't expect any. I plan on dropping in the original filter whenever I clean my K&N one.