There's one other POP3 command that it might well be worth knowing if you have to manually check email on a regular basis: the TOP command:

TOP msg n - retrieve the top n lines of message number msg. Note that TOP always returns the headers plus the number of lines you specify, so to retrieve headers only just do TOP msg 0.

I find this one particularly useful when I'm on a slow modem connection and find that one of my friends has decided to send me a 10Mb email from his work account on a T3. You can simply telnet in to the mail server, use TOP to find out whether you've been mailed something good (unlikely) or pointless (usually) and act accordingly.

Just a quick FYI, the full set of POP3 commands are documented in RFC 1939.