I really love the idea of tahoe-lafs, even though I never really got around to setting it up myself...
So why not? Serious question -- I'm sure there are good reasons why you haven't, and I'd like to know what the number one reason is.
First of all, Windows (server).
Then, to make "real" use of it, I'd need to convince a few friends of mine to install and use it at their home servers too (most of which run Windows as well as being a bit more "illiterate" with computer stuff than me) to form a grid. Also I'm not 100% sure how to set up the access point to all of this (introducer or something like that?!) so it'll be reachable for me and them in a secure way if I'm on the road or behind a NAT in an internet cafe. I'd probably even have to rent a VPS machine for that and they come with bandwidth limits.
Also Sparkleshare and Owncloud (even though they have some quite different architectures in some aspects) seem to become more interesting with every release to me.
I also am not sure if/how multisourcing (like BitTorrent, getting 1 file from several (DSL - upload limited) lines), streaming of file content while still downloading and deduplication are implemented - and just for sharing documents, Dropbox is simply easy to use for "noobs". I also don't know if tahoe already prefers nodes on a LAN to get parts from, or I risk downloading large amounts of data from friends, just because the scheduler does round-robin or so.
As a last point I'm always a bit paranoid when it comes to key files that I might loose, but that I shouldn't toss around on any online hoster account I own either... Having an encryption key derived from a password (similar to Truecrypt) would make me feel more comfortable.
It could be that some of the things I mention are already fixed, it has been some time since I last checked the page (I have a list of projects that I take a look at every 3-6 months or so). Hope this helps you to get a better view on some things that I as an "outsider" to the project perceive.