i've also heard horrible things about them. one guy said that after running one he could wipe the fine dust outta his throttle body with his finger. it was actually part of a big argument that he was having with a K&N rep on another forum. weather they work or not, don't think i'd ever put one on my machine.
Hard to say, I've heard both arguments. I've had one on my truck for about 5 years now and love being able to clean it every year and not have to buy a new filter. As for letting more dust and debris in, I'm not sure. I could see there being issues if too much oil was on the filter and it affecting sensors. I personally like them, but you have to install and oil them properly. Anyone else a fan? If not, do you stick with oem filter?