I hate yellow jackets, which I have also heard called ground wasps, since they are in the wasp family. I got stung by one last time I was out riding. I was moving down hill too, I dunno how it got me. I see them everywhere though, especially this time of the year.
I just installed Avid BB7s on my 29er SS. I changed everything with them. 185 up front and 160 in the rear. Alligator Fortress brake cable kit and Avid Speed Dial 7 levers. Love this setup. I would definitely recommend changing everything.