I gave upspin (the project that started at Google) a go but I found it a bit buggy. My dream with be to have $HOME be available in multiple machines, so that I can log in, start my text editor, my terminals, and everything in between, and they all pick the right configuration. If anyone is aware of such project or would like to build one, please let me know.

Of course, it must be more than just rsync, and it needs to be smart about file downloads, caching when necessary, but also not bloating machines when one is only curious in a subset.

EDIT: Forgot to mention, should ideally be open source.