1. I saw one last week advertising a halloween party, so it's been in the ground for over 6 months. It is on a sidewalk near the university and is passed by about 1000 people per day, and in 6+ months not ONE SINGLE PERSON said "Oh, I should talk this down".
2. I once saw a city employee get off their riding lawn mower to move one of these signs out of their way, cut the grass, then get off the mower again to put the sign back!
And echoing the GPs comment, what really gets me about these is that we all have our lives diminished so that one person or company can earn a little extra...maybe. Or in other words, 1000's of people are subjected to this and perhaps 1 person might bite?
I'll close with my favorite interpretation of advertising: Advertisers essentially steal your sense of self-satisfaction so they can sell it back to you.