Server Population Average?
Shiva is the second oldest server, so our population is higher than most. However, since a majority of the players are JP the peak time is during JP hours
Server Population on Weekends?
More than during the weekend? :) I'm not really certain of percentages, but like any game the population always spikes when more people are available to play
NA & JP Friendliness?
I have only encountered a couple of JP vs NA tiffs. I don't think those dealt with the standard JP > NA misperception, either. Instead, I think it was just because the people involved were asshats who thought that they > everyone else.
AH Pricing?
Mostly stable economy. Some items are way more than other servers, some are way less. However, everything is proportional. Sure, leaping boots may go for 800k, but then again a stack of silk thread goes for 20-30k.
Getting Parties?
Completely up to your job, your abilities, and who is available at the time. I don't think that these stats change on any server.
As far as the people go, we have our troublemakers but we are mostly a good camp. HNMLS tend to fight too much, and we have created some of the best bots the entire server set has ever seen (although no one will admit to using them). Then again, there is almost always someone willing to help you do anything you need to do. I wouldn't want to move :)