When and how is this Stack Exchange going to get a logo? #5 on this blog post clearly says we should be thinking about this. Is Jin Yang going to make it? Am I jumping the gun since we don't yet have a non-stackexchange domain?
I don't believe there's any harm in discussing the logo, certainly, if anyone has any designs they wish to put forward, I would be very interested in seeing them.
It is a tad early. I'd worry more about the domain name, since that will tend to color what the logo becomes.