Hallmark: When you care enough to do the first thing that comes to mind.
Sure, there was always something less than satisfying about receiving a card for your birthday--unless, of course, it was from Grandma, which meant it would reliably hold a five-dollar bill or check. Even when the Solipsist was in his late-twenties, the amount was seldom more than ten dollars. Yes, it's the thought that counts, and, no, the Solipsist is in no way criticizing his late grandmother. Still, it was amusing.
But that's not the point. The point is that, nowadays, it's probably a sign of deep affection when someone sends you an actual card. When most responsibilities can be fulfilled via online activity, there's something quite touching in the thought that someone actually went out--to a STORE, no less--and looked through the offerings before selecting something just for you.
And what's the etiquette on e-cards, anyway? A "thank you" would seem to be in order, but how much of a thank you? Especially when the card arrives on the actual day. With non-virtual cards (i.e., cards), when they show up on your birthday, it at least suggests that someone thought of you ahead of time--in fact, if the card was mailed, it guarantees such thought. The e-card on your birthday MIGHT mean that somebody thought ahead and arranged for the card to pop up in your inbox on the blessed day. Or it might mean (let's face it, probably does mean) that somebody went into work, flipped on the computer and, in between hands of computer solitaire and Facebook updates, had an "Oh, crap!" moment and quickly went to BlueMountain or its ilk in a last ditch attempt to avoid condemnation.
(Digression: BELATED virtual e-cards must be the ultimate sign of laziness. End of digression.)
The Solipsist's advice: Be gracious, be thankful. And he's not just saying that to prepare you for your birthday presents.
********************Guide to Dathonian English:
Use the force, Luke: Concentrate; Pay attention.