if I'm interested to send a private message to a certain user from serverfault, how can I do that?
This has been discussed ad-nauseum on Meta Stack Overflow (where Stack Exchange itself is discussed) and has been declined (several times, if I recall correctly).
See this question on MSO for excruciating detail.
Server Fault does currently however have a chat room going on http://chat.meta.stackoverflow.com . If a person wants this sort of thing that is probably the place to go hang out (Closest you are going to get).
Of course that's of very limited use to those who work in different timezones. Aug 25, 2010 at 4:55
1@John Gardeniers: Pfft... only if you sleep... Aug 25, 2010 at 13:05
@john but the chat room is stateful, so assuming there aren't thousands of messages per hour (depends on the room) hopefully people will be scrolling back and checking to answer. Sep 5, 2010 at 22:04
My take on this is that anyone who cares to be contacted has numerous ways to provide contact information for others to find. e.g. Email address or other details on their linked web site. Anyone not making themselves fairly easily found probably doesn't want to be contacted.