I'm waiting, personally. The exclusivity deal, complete lack of communication on when we'd actually get it, the fact that numerous game-busting bugs are still present (like random vampires attacking towns and wiping out tons of NPCs), the way the last two beta patch periods have gone on PC, and the fact that it's $20...meh. If you're on PC (which I assume you are, since you're asking about this today), I'd at least wait until the USKP gets a Dawnguard component out and some of the nastier bugs are quashed.
20 DOLLAR is not 20 EURO! God dammit!
20 eruo = 24,43 US dollars!
I have a feeling Kaelin was linking you to that thread for a discussion on whether or not Dawnguard's worth purchasing, not to debate the current U.S. dollar to Euro exchange rate. Calm down.