So I've been learning about how the voter registration works here, and wow they do fun stuff in the name of removing 'fraudulent' voters
One thing they can do is send you a letter, and if you don't respond, well you're off the able to vote list. Simple enough...
So the Parties can initiate this and the facts according to the people behind http://www.stealbackyourvote.com run something like this.
You're the republican party, you get a list of people who have had the mortgages foreclosed (they're unlikely to vote for you) you send them one of these letters and it will go to there old residence as they are extremely unlikely to update there address as they're probable in temporary accommodation. Bingo one disgruntled household of voters no longer in the system.
In a radio interview they mentioned that this was also done to US soldiers who strangely enough couldn't reply as they were deployed. Yay.
In Colorado one in five registered voters have been removed.  Now there were probably some real removals in there, but wow.

You can also watch the bbc reports he files at www.gregpalast.com/