In one sense you could say that every question here is a poll. After all, people vote for the answers they feel are helpful.
I tend to use the term "polling" in a different manner though. For me, the difference is in whether the question is looking for answers or items.
A question like Recommendations for 6-player board game is explicitly urging folks to answer with one game per answer. That ends up with people voting on individual games and awarding reputation for being the first person to mention a popular game. I call these questions polls and now actively discourage them.
A more recent question, Recommendation for D&D players who want a faster dungeon/questing game after dinner? has garnered a couple good answers. The answers by aramis and gomad contain multiple games each with some explanation about why they feel that game meets the questioners need. The extra detail allows the voters to be better informed as to whether the answer might be useful (and deserves an upvote).
The number one item on the famous Good Subjective, Bad Subjective blog post is to encourage answers that explain themselves. I think the whole list is worth republishing here.
- Great subjective questions inspire answers that explain “why” and “how”
- Great subjective questions tend to have long, not short, answers
- Great subjective questions have a constructive, fair, and impartial tone.
- Great subjective questions invite sharing experiences over opinions.
- Great subjective questions insist that opinion be backed up with facts and references.
- Great subjective questions are more than just mindless social fun.
The second aspect of your question is also answered here. Using a poll from another site to back up an answer is encouraged. Which of these two statements would you prefer seeing in a question or answer?
- "Everyone knows Russia has an advantage in Axis & Allies"
- "According to a recent poll on Axis-allies-experts.com, the top players feel that Russia has a significant advantage by a 2-1 margin"