I saw an internet poll in my local newspaper today, the question was "Does Chick-Fil-A donating money to anti-gay rights groups make you more or less likely to eat there?"
The results with about 200 votes:
51% More likely
33% No effect
16% Less likely
It didn't surprise me much because it's a moderately sized southern town, there's like 4 chick-fil-a's within 10 miles so I wouldn't be surprised if a tenth of the population was employed by them, and the skew due to population sampling (who reads online newspapers? I'd guess mostly people between the ages of 30 and 50, slacking off at work).
I don't think a boycott is going to be especially useful because I'd imagine most of the people wanting to boycott it probably don't live near once, since the chain is highly regional. I also wouldn't be surprised if people picketed the one in Manhattan and made national news. Not CNN headline news, but maybe CBS 10 o'clock "we're covering the chick-fil-a story and decided to show some protesters for balance for our the national portion of the local news where we play syndicated content from the CBS mothership" headlines.
