I very rarely give gifts, but if I do, prefer "just because" ones - partly because I don't know my friends' birthdays, and my sister and I don't bother about our birthdays at all.
From time to time, I have been known to do that. It puzzles the snot out of Michele when I do. Once, while on a road trip, we stopped at the Fenton Glass factory, and after the tour, went through the gift shop. I saw a Swarovski crystal butterfly, and waited until she was distracted, then bought it and snuck it out, then gave it to her when we got home. I don't do that all the time; just often enough that it doesn't lose the surprise factor.
I love both giving and receiving just because gifts. There is no obligation or expectation involved just a little something that someone really appreciates.
Sometimes I do a just because, when I come across something that's just absolutely perfect for someone. For example - I was speaking at a conference on the other coast. One of the vendors had a fantastic dragon. And Himself really, really likes dragons. So I bought it and had it shipped. Not only was Himself especially delighted, he found a fantastic place to display it
Yes, I enjoy giving gifts that are unexpected. Usually for someone who is not feeling well or has been going through a rough patch. It not only surprises them but lets them know someone truly cares.