Mike is trying to lead you astray! If you've never seen them before, watch them by release date. Otherwise, there are in-jokes in episodes I-III that won't make sense. Also, viusally you'll get a real jolt going from Epsisode III to Episode IV - you'll think the universe just got knocked back to 1978. Oh wait, that's exactly what happened.
But the biggest reason to watch them by order of release date, in my never-to-be-humble opinion, is that the end of Episode III packs a much bigger emotional punch if you know what happens at the end of Episodes V and VI.
Fun fun fun! Back in high school, my best friend and I tried watching all three original movies (on video, back before any special edition anything!) in one night. Di should remember this one. We only made it to the end of Empire Strikes Back, by which time we were getting pretty darn punchy. We were making up skits wherein Darth Vader was grounding Luke for getting snitty. Of course, we thought it was comic genius, but when we tried to demonstrate that genius to our friends at school, they just thought we were weird.