Wirelessly posted (iPod touch 32GB: Mozilla/5.0 (iPhone; U; CPU iPhone OS 3_0 like Mac OS X; en-us) AppleWebKit/528.18 (KHTML, like Gecko) Version/4.0 Mobile/7A312g Safari/528.16)
Smart mailboxes every time. That way I can archive my mail by date and still keep related mail together. It also means that when I pick my mail up on a remote device it's where I expect it (in the inbox!)