Wow, that site is a total joke.
There are some reasons not to use Vista, but these aren't any of them. It's pretty funny seeing them say that "when you legally buy Vista, you don't own it." considering that applies to ANY software, not just Vista. Even console games.
The throw the DRM word around due to the negative connotations associated with it, but they make no connection to Vista whatsoever. You pirates need not worry, you can continue your looting in Vista.
If you guys hadn't noticed, this site is written by open source zealots. They want you to sign a statement supporting a society based on free open source software for crying out loud! There are no real facts in that website at all.
In reality, compared to XP there is nothing wrong with Vista aside from a lack of drivers for older hardware and it being a little more demanding under the hood(which is to be expected, just like from 2000->XP). Personally I use XP and OS X, but if I bought a new computer with Vista already installed I wouldn't care.