I'm sure there will be differing opinions on this one...
http://news.motorbiker.org/blogs.nsf/dx/tapcaps-using-gloves-with-touchscreens-on-your-motorcycle.htm
http://www.thetapcaps.com/
http://news.motorbiker.org/blogs.nsf/dx/tapcaps-using-gloves-with-touchscreens-on-your-motorcycle.htm
http://www.thetapcaps.com/

Can't be helped? What's more important on your GPS/PDA, that needs your attention immediately, than riding the bike? Another gene selection scheme?