My pet peeve is people who tag their polls in a way that would bias their sample. Like, for example, if you make a "how much do you like anime" poll, and tag it as "anime", then it's going to be shown to disproportionally more people who strongly like anime, since those are typically the people who browse this tag. Sometimes it doesn't matter, because you may only care about the opinion of people who browse certain tags, or the poll isn't supposed to be serious. Or maybe you just want qualitative data. But if you want to get a sample that is representative of a larger population (of Tumblr users who do polls for fun), or if you want to interpret the results as if that was the case, then you have to keep tag-induced sampling bias in mind.