My main reason for liking slip-on's is for the sound. I had Yoshi slip-on's on my '01 R6 and '06 R6s, they sounded great.
I just put a Yoshi on my '07 R6 (high rev) and I think it pretty much sounds like the stock exhaust.

Is it cause it's a shorty? Or the bike? Or did we do something wrong on the install?
I am really disappointed with it.