I'm in the tacky camp. Not deliberately, and not thanklessly.
I suppose procrastination isn't too far removed from laziness. It just sounds better to say that you're a procrastinator and not bone lazy about these things. I'm speaking of sending handwritten thanks....
But we are in a different world now than the one we grew up in (if you're old enough to remember pre-electronics ) and I have to agree with Seed, an email or text thank you is a thank you, so take it as such and be happy about it.