tivo_installer_0.6 left both of the TiVos on which I tried it unbootable, permanently stuck at the "Just a few minutes more ..." screen. I've since solved the problem and got them working again, but if anyone else has the same problem (and I don't yet know why I had it, or why everyone else doesn't), this is why:

The installer makes a symlink in /lib/modules (i.e., /tmp/tivo_mount/lib/modules from computer running the installer) for router.o pointing at routerplus-2.4.20.o and a symlink in /tvbin for tivoapp pointing at tivoapp.patched. Go into those directories, remove the symlinks, and either rename routerplus-2.4.20.o to router.o or make a "hard" link for it, and similarly for tivoapp. Then it boots, and it's possible to ssh into it and look around on the running TiVo. What I found is that trying to list the /hack/bin directory results in a couple of pages full of "Input/output error" followed by the listing with all the symlinks (i.e., most of the files in there) broken. They can be fixed manually, and then everything runs smoothly (almost: there are some files in there that should be executable but aren't; chmod a+x /hack/bin/*). I don't know why symlinks created from the installer system fail, but that's why it wouldn't boot initially. (When I get my other boards back (currently out getting chips replaced), I'll fix the install and then put a drive back in the computer and investigate further...)