K&N Air Filter Opinions

I use a MAC CAI....and I feel the difference in acceleration when I take off than the stock Air Intake tubing / filter.

I have the Mac CAI, it looks cool but thats about it. It's a real pain in the #ss to clean the filter, as it's in the fenderwell. Testing with the G-tech Comp. there is no difference in 1/4 mile times with and without.[I took it off, and just run the stocker with a K&N filter] The K&N filter will not work on the Mac CAI, not sure about any of the others, but most CAI come with a filter. If you do a search on CAI you will find mixed reviews, but the general consensus is, if you must buy one, get one without the sharp bend into the fenderwell, as the bend can cause the MAF to get inaccurate readings. It does make a cool turbo-like sound though.
Edit: Keep in mind, just b/c it didn't help my 1/4 mile times, doesn't mean it won't help yours, every car responds differently.

get a universal 4" x 9" filter and drop the airbox. i was really surprised the difference it made when i was not expecting it. it felt more responsive and really felt like it was getting more air easier. i recommend that instead of a drop-in style.