I actually haven't decided whether I'll be listening to the single or not. I think mostly likely, I'll listen to it once or maybe twice. I know people are responding to declarations of this variety with "you won't have the willpower," but I actually think I will. I fully fell in love with Dream Theater in December, and I spread out buying the albums over the last 8 or so months. In fact, I only just got When Dream and Day Unite and Falling Into Infinity and have yet to listen to either (I'll probably do one tonight and one tomorrow). I don't want to ruin the impact of the album by being very used to one song in advance; however, I had heard OTBOA once, several months before getting ADTOE and it didn't really ruin it for me. I think if I listen to the single once, I will be able to balance satisfying my curiosity and not ruining the album in advance.
As for snippets, I will avoid those like the plague. I don't want to be going through the album for the first time identifying all the parts of the song I had heard before.
I will read people's comments on the single and the snippets (if those come), because I've done the same for the other albums before I got them and there were no negative impacts, but I won't be listening to any snippets and will keep my listens of the single to 1 or 2.