Wikipedia’s mobile site has been officially launched and running on a new server (in Ruby!).
Currently the site supports four mobile platforms: iPhone, Kindle, Android, and Palm Pre. Only the English and German versions are up, but support for more languages is said to be coming.
If you visit a Wikipedia page from a supported mobile device, you will be automatically redirected to the mobile version. You can click through to the regular page for editing or accessing other features not included in the mobile transcoding (e.g., history). You can also permanently disable the mobile redirects for your device, if you like.
You can get some idea how the page rendering is simplified in a non-mobile browser by looking at a page like http://en.m.wikipedia.org/wiki/Alan_Turing. But the device specific encoding makes this work much better for each device.
I like the way it looks on my Palm Pre, which differs from the iPhone encoding, and think it will make Wikipedia much more usable from it.