Are you sure it didn't also have to do with the slew of bad press they received for a while, especially here? Do you actually have a memory of avoiding groupon and at that time remembering the ads, or are you now remembering avoiding groupon because you disliked them and now remembering the ads? (I ask because I find perceptions of past actions interesting, not because I specifically doubt you).
I am aware that memory plays tricks over time, so I am not 100% sure, but I have a distinct memory of sitting at work and getting seriously pissed off at the astounding amount of same, ugly, pink Groupon adverts I've seen in the space of few hours. I recall how ridiculous a lightweight-layout site looked when all available ad boxes got filled with variants of the same animated pink ad at the same time.
I'm pretty sure (let's say ~80%) that it was before I started hearing the bad press about Groupon. I recall being initially biased against them because of ads, and then slowly learning more reasons to not participate.
It's really just perception of your brand. If you advertise to me I'll think less of you. Maybe that's enough for me to avoid you, maybe not, but it certainly didn't help your cause.
