I remember when Mormon had a rewards program where you got points by accomplishing "missions" on their site and through click referrals. That itself wasn't annoying, but it was ended abruptly and a lot of my friends didn't get to cash in on their points.
The other campaign that annoyed me was Something Rotten (especially its sponsored stories), but I liked it more after I saw the show because I wished the show had been half as creative as the campaign.
"This thread reads like a series of White House memos." — Mister Matt