OMG i didnt think people still did that anymore, I remember doing that on my first car, and all my mates and if you dropped a K&N filter in it sounded like a fighter jet. My old Orion 1.6i sounded sooooooooooooo good especially going through tunnels.
Always used to be Corsa's and saxos that sounded like V8's.
My mate had a 1.0 Saxo with a "Tuned" air box and a Peco BB4 back box. he'd drive past and people would be looking to the sky, then about 30seconds later he'd go past at about 15mph trying to get up to 30mph 
How we laughed!
As for performance the only time i ever noticed a problem was on a really hot day sat in traffic and then planting it but after a few mins it was fine again.