A dialog goes something like this: Player A: I live in X time zone and 3pm works for me. Player B: OK, I'm in EST, let me see what time that is for me. ... OK, that works!
And then Player A and Player B miss each other, because Player B wasn't aware that his current time zone was EDT, not EST.
Even if both players convert to UTC first it doesn't work, because EST -> UTC and EDT -> UTC yield different times. And it's difficult to help them out with site-mandated time tools, because players like to coordinate over IRC, Twitter, GChat, ...
I'm sure there's a good way to fix this problem, I just feel like I shouldn't have to.
EDIT: I just saw the Eve online comment. Unfortunately that doesn't work quite as well for us, as the game isn't a program that's always running on the player's computers. It's more in the spirit of trying to coordinate chess matches.