I haven't used MySpace much for years now anyway, so the answer for me was simple: leave.
If you're in the same boat ... make sure you actually edit your user data before deleting your account. Change things like your First / Last name, home town, etc to "PRIVATE". Delete your photos. Message your friends and then un-friend them. If you just delete your account or set it inactive then all that does is stop you from logging it in, but in theory (who knows what their practice here will be) the data will stay in their systems. If they're going to sell your data ... give them bad data to sell.
Take this as a warning Facebook and Twitter ... if you sell my data I will pollute it and leave. I don't care if you set up ad targeting systems so that the ads I see are relevant to me, but don't be turning into the next generation of spam lists. That's not what I signed up for.
