I hear the same
The upsides (at least in my opinion) better performance (maybe) and better sound of the car
Downsides - If you are going to go with something self made or something cheap (like on eBay) your car will not pass the smog check. I think they require some sort of a stamp on the intake in order to pass the check... The work around is to keep your original intake and right before taking your car for a smog check, swap them out. I know it is a bit tideous, but it works

Good luck!

dimaj