Wiki pioneer SocialText today released a version that's smart-phone friendly. I tried it on my Treo and found reading wikis much easier on the small screen than it was when I used the Treo to access the full PC-size SocialText interface. Unfortunately, the editing window was about four lines high by 20 characters wide, far too small to use--it's like looking through a soda straw while painting a landscape on a full-size canvas. CEO Ross Mayfield (video link) showed me the same site on his BlackBerry, where it looked and worked much better. And as he says, most of SocialText's corporate customers are "crackberry heads."
Wikis are great tools for collaboration, but even though most of them are fairly simple to navigate, their user interfaces are designed for full computer screens, which means, if you're a businessperson who relies on a wiki, you can't get much done on it when you are out of the office, working on your BlackBerry or Treo.