I do actually find it offensive.
I'm not so much offended by the thoughtless individual using the phrase, but the fact that it's becoming a common phrase. the people who say this probably don't give it much thought, but the phrase undoubtedly states that: gay = bad.
not really very progressive, especially when young kids start picking up the phrase, and they'll learn the meaning of the word gay as something lame/negative, before they learn its' other meanings.
another point is double standards. People are so careful about saying anything that might sound racist or attacking someones religion.
It wouldn't be as widely accepted in public to use phrases linked to other population groups like jews, or blacks or muslims, as a general derogatory phrase.
Only people who hold extremist views actually do that (and mean it).
Curse words like Shit and Fuck are bleeped out on tv.... words like that don't offend whole population groups, and are politically neutral, so I find them much less offensive than someone saying "that's so gay".
I wish people would use the word in its original meaning, I know I will.
Have a gay ol' time everybody!