Nowadays, I'm very particular about what I sign up for. Once in a while I go through my gmail account (with about 800 unread mails at the moment) and unsubscribe from anything I haven't managed to read in the past year, no matter how much I really wanted to get to doing so.

If a poll does not let me sign in with Facebook/Twitter/LinkedIn/etc. I generally close my browser at that point.

These guys did a very neat poll recently for programming languages:
http://code2013.herokuapp.com/?elq=44d2e43369514fa69a86c4ffef4bd2ed&elqCampaignId=1025

You post to twitter to vote, and they count the unique hashtags so the whole thing is very transparent.