One advantage to Gmail is that when you use the web interface to send mail, it doesn't put your IP address in the headers (it does include tracking information that Google could presumably use to get the actual IP). This is useful when travelling internationally -- my parents' Yahoo messages to my sister while cruising in France got blocked and/or sent to a spam folder (from an account that they use to send us email all the time). I'm pretty sure this was because the IP of the client connected to the web was in the headers and resolved to a location outside the US.