Ha, brought me back. I personally remember hating my fixies as a kid, having to take your feet off the pedals as they spun around madly on the downhills in a park near my house, no way to stop. Probably why I still love cycling.

I haven't done much touring, but I do a lot of vicarious touring at crazyguyonabike.com, and it's more a test of will power than anything else.
What's the longest ride you've ever done?
You can overcome the ups and downs on a fixie on short rides, but what kind of legs do you need for days in the saddle, trying to maintain a cadance that doesn't make your legs burn? I think a great fixie for such things (I may catch he!! for this) would be the Rivendell Quickbeam, a great SS/fixie, all the simplicity, freedom, pleasure of a SS, but with the convience of a 4-speed and geared if properly, enough bike to get you anywhere. Also, touring bikes are so darn heavy loaded anyway, would a rear derailluer really make a difference?
If you go, Good Luck!
Adam