It's not the end of the world, but I thought it was pretty irresponsible.
I think musicians/entertainers should keep their political opinions to themselves unless they really know their stuff and are prepared to support their opinion when they voice it. I.E. actually "change people's minds", rather than lead them blindly into something (intentionally or not).
Hopefully every fan old enough to vote will inform themselves and make their own choice rather than voting for whoever their favourite musician asked them to. Yes, I know that's a niave hope.
-Kev
Edit: FTR, I think it's a good idea for any artist to use their position to encourage voting in general. Just not specifically one party/candidate.