If your ISP is using POP-before-SMTP as a way of closing their SMTP servers to unauthorized relaying, you may have a slight latency problem if the POP server isn't on the same box as the SMPT server. My ISP (pair.com) usually takes 2-3 seconds, but sometimes takes upwards of 10 seconds to relay the right message from their POP to their SMPT server.

It takes all of one line of script to work around this. The annoyance was mostly in discovering this behavior.