Not a whole lot of gain IMO to more zones open, but as far as static zones, they do, on my server at least, cut the load time in to "city areas" by a fraction of time. Sorry for being late to reply, but NOS put things in perspective here.
I will add though, that on mine I have noticed that when my zone servers start to boot up, it sends a request for all of them at once. What I am getting at is, mine is set for 15 dynamics, and as that zone server starts up, it sends a request for all 15 at once to the world server. Seems to cause them all to crash from there, and then auto boot kicks in and regains them, one at a time...like normal. No idea if anyone else has seen this, or knows where a timer switch may be that I could have some how modified. With the auto reboot of zones, I could care less, but this does add more time to a full boot of sequence of my server. With Nightravens examples, I'm almost willing to say his takes at least a good 5 minutes before things calm down a bit.