what about a lenny snapshot?
stabilise +/- and target a snapshot release.
users would apreciate and make testing more popular.
this could be a propose to put to the DPL/RM's ... no?
I do know Debian usually DOES have testing snapshots available for download. However, they haven't done any in a while due to debian-installer issues...
I would say, though, that the big problem with using testing as a desktop distribution is that, as of now, the testing transition process can cause problems. Most notably, testing tends to lag with respect to security updates compared to stable/unstable. Also, sometimes packages that fix important bugs are kept from testing due to issues such as a failure to build on obscure architectures. This is probably the best place to investigate to make testing more usable...
However, IMO the best approach would be to make backports an official part of Debian - long release cycles aren't a big deal in the case of most packages, but being stuck with a kernel that doesn't work with your hardware or a way-outdated Firefox/Iceweasel makes stable somewhat of a problem at times...