I use it all the time. I've ended up treating my Wii as a virtual arcade machine, downloading titles I've missed and also titles that I own on older consoles that I no longer have hooked up to the TV due to spacial or technical limitations. I think it's a great system, one that I hope never goes away from Nintendo systems. When in-console Nintendo harddrives become massive and the systems are more capable, I'd love to see further generations of titles available.
As a child, I played tonnes of games, but only had the cash for a limited few. It was usually the rule that if a friend owned a game, then I shouldn't buy it as borrowing cartridges was a common event in the school yard. The only games that I had that overlapped other people I knew were the Mario series. So, while I played through other titles to their fullest, I missed out on owning some like the Super Star Wars series, the recently VC added Indiana Jones SNES title, and -- *gasp!* A Link To The Past. I now have my library updated to include all these great titles. It's wonderful nostalgia, through and through!
Recently, I've taken to downloading the free WiiWare demos. Great stuff, as I'm trying games I otherwise would have overlooked . They are great fun, but it does help me come to the decision that I either don't see myself buying that title, or to pick it up. One demo play got me to purchase a title I otherwise wouldn't have, so -- bonus!