How many companies collect date of birth as part of their registration process? You have submitted yours to at least a few dozen, but possibly hundreds, from MySpace and IM programs to banks, dentists and retirement plans. How easy is it for them to set up a small script that would send a "Happy Birthday" email to each client once a year? Very easy. Maybe an e-card. Or even a coupon or two.
This is so obvious that I thought everyone was doing it and it wasn't worth writing about. Apparently not -- Cirque de Soleil's was the only e-card I got (a few weeks ago, but it only occurred to me now) from someone to whom I am a customer. Of course, I'm not horribly offended by this lack of attention, but the Cirque's card was a very memorable even if auto-generated touch.