It's about the colorful and shapely foliage, not the flowers. From Bridgewood Gardens, on Why We Grow Hostas:
I'm not a botanist, I don't know the science. But I do know that hostas have some kind of chemical in them that makes people nuts. I know people who have normal size houses, with normal size back yards, normal kids and a sensible spouse, and these people grow a thousand or more different kinds of hostas. I don't know just one of these people. I know a bunch of them. These people are obviously nuts and they have only one thing in common, they've all come in contact with hostas.
Obviously, there are still people who add a few hostas here and there to their gardens and leave it at that. There must be some kind of threshold you have to cross - one day you're a sensible gardener, the next day you're nuts. I think the first sign of trouble is when you say to yourself, "I wonder how many of these things I have now."
So you count your hostas and you're surprised to realize that you already have 40 different kinds. You don't remember buying that many, you never thought of yourself as a collector, it just sort of happened.
Read the whole thing about Hostaphilia.
Our first post about Hostas was Hosta City. I think Hostas are OK, but it's the Mrs. who is the enthusiast and connoisseur. It takes them a year or two to get established, but after that they are tough. Few things are more pleasing or rewarding to grow in deep shade, and they are so dense that you get no weeds. Hosta Direct has a large selection.
Photo on top: Hosta "Captain Kirk"