The only negatives I've heard about K&N air filters has been occasional mentions on message boards like this. The first link you posted was the website of an Amsoil dealer. Hardly what I'd call impartial. I didn't feel like wadeing through the whole thread of the message on your second link,not worth my time. Neither is this argument. I've heard similar bad things (on rare occasions) about Amsoil or other similar (synthetic) products. People will have bad experiences after changing oil, filters, etc, and blame it on the oil or filter, when there were other causes.

I just went out in my shop and looked at several of the K&N (and paper) filters I have laying around. Nothing what I would call rather large holes. If there are rather large holes in any filtering product, it is damaged and should be replaced. A properly cleaned and oiled K&N air filter will not let anything through that will damage an engine.

Discussions like this are why I remain an Amsoil "prefered customer", and not a dealer. I used Mobil 1 oil in practically every engine I had for the last 10-12 years until I decided to give Amsoil a try last year. I really couldn't tell any differences or improvements or problems with any of our three cars after switching. There are a lot of good products (oils, filters, etc) on the market, heck, a lot of people have gotten 200k or 300k+ miles on cars with conventional dino oils and paper air filters (including the previous owner of our Volvo). It is the attitude of a lot of Amsoil dealers (not nececcarily you) that makes me strongly consider switching back to Mobil 1 and other lube and filter products for my cars.

-Keith
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1990 245 --- 240,000 miles and still going strong