Have been sending e-cards through Corbis for several years with no problem at all. Mostly they offer that service to promote the sale of their prints, which are numerous, and quite lovely. They don't send an attachment, but a link to your card, so it doesn't muck up any servers. The photos are high-quality, not that silly animated stuff that other sites offer.

I prefer sending paper cards, but sometimes you need the sentiment to get there faster.

Some folks like to talk on the phone, and that's okay too. Personally I detest it, as do a couple of my friends, so I write instead. Just a different way of communicating. I think it is all right to send cards or not, however you see fit. :-)