Gmail's implementation of IMAP is quite broken (and the XMPP/Jabber one too!). But you can achieve a local setup which rivals with Gmail by combining mutt and/

Gmail's implementation of IMAP is quite broken (and the XMPP/Jabber one too!). But you can achieve a local setup which rivals with Gmail by combining mutt and/or notmuch/mu and isync (mbsync). And it's quite possible to keep it sync'ed with Gmail, although there might be some rough edges. Personally, I don't thing tags are that useful if you have a fast and expressive local search engine like notmuch or mu (xapian-based), but YMMV.