Don't copy over all your hidden files - ones that start with a dot. That will corrupt your new system and it'll fail to boot.Archiving my home directory as a tar file is exactly what I was gonna do.
Some are worth saving, .mozilla contains your Firefox profile with all it's saved logins and passwords, bookmarks, etc. Caveat with copying that one to a new system - if there's already a .mozilla folder in the new system you Must delete it before copying the old profile in, overwriting the new one doesn't work.
If you use Thunderbird for email then the .thunderbird is safe to copy over as well.