4) Voter supression. I've been scrubbed from the roles before, and found out about on election day. It sucks. If I had been on the edge about voting because of (2), that experience probably would have been enough to push me over.
I have voted in every election, local state and national, since 1992. I have voted absentee since 1994. If you have the ability to set it up, do so... because they can't purge you if you've been voting regularly.