haha, yeah it does make you wonder - but if they have say a couple million legit email addresses of people who signed up that were interested in photoshop they can make a pretty good return on their investment (10 Photoshop Licenses) by sending one email a week and selling ads in the email to photography companies. Nothing really Spammy or illegal about that, but quite valuable to them.
I don't know how many ad emails flood the inbox, I just sent my email in for the Photoshop draw today (I don't have previous experience with appsumo). I have so much spam as it is, another 1 or 2 a week won't be too noticeable
