The cleanest solution I've found is *not* to have a shared home, due to the configuration problems mentioned above. What I have is a separate partition for my data, mounted as /data in each installed distro. /home/mugstar consists largely of symlinks to directories on /data: for example /home/mugstar/music is a link to /data/music, and /home/mugstar/.mozilla-thunderbird points to /data/.mozilla-thunderbird (which gives me access to my mail regardless of which distro I boot into). /home.kde, and other config files, are not symlinked, and therefore stay untouched by other distros.
If you go down this path, you *must* ensure that *both* your username and your numerical user ID (UID) are identical in both distros. If you don't you'll run into a nightmare of mixed up permissions.
Distros differ in the default UID's they assign to a new user - some start at 500, others 1000. Some will allow you to manually set a UID during installation, others don't. For those that don't, create a test user first to see what UID the account is assigned.