Dave, it would be wonderful if you would play with a Time Capsule when they are out and let us know how it goes
Thanks to your feint praise of the Airdisk attached to last year's Apple Airport Extreme, I held off buying one, and quite glad about it too, now.
If you are just looking for a network home for sparse disk images, I can recommend the Simpletech Simpleshare 500 GB. It is quiet, low energy, and with a bit of help from an Applescript that makes sure it unmounts when SuperDuper! is done, it has worked very well for the last six months. It was cheap, too. Sadly, it seems to be out of stock everywhere now.