Just move the mouse to the member name, you will see his name with some number .html in the bottom (link). (his/her profile page). You can even click and see if that is not showing at the status bar. Mostly it is created by the order of joining. 350Z is no.2 :D
If they delete the banned/ test user name, the database normally do not remove the numbers. It will be almost same /equal to the user name (even though the no. of users are less). 10,000 is the actual users (not including banned users i believe) . Again, I may be wrong
It is Administrator account /test account created when the vbulletin installed. Normally No.2/3 is actually the First user :)
Congrats to all of us and 350z especially! This is a mega milestone - our forum has always had an approach for being for the people and by the people. Its just a beginning and we have grand plans - its the people(members) who make a good forum, thanks to one and all!