I replaced the header gasket on my bike this afternoon after work. ( of course I rode to work ) Man... What a difference. The throttle response is much tighter, I don't smell exhaust when I sit at a stoplight. I must have really been due for a replacement because it really made a noticeable difference. I just did it on a whim after I started to notice a little soot around the exh. port. I figured after having the header loosened up several times to do muffler mods ; and eventually changing the muffler I thought it might be comprimised but I never imagined after changing it what a diff. it would make. Comparing the 2 when I had the old one out... it was really in bad shape

Yeah, I was pretty amazed on mine too.  And it cut the pops/backfires down to almost nothing too.