Basically she's done all the number crunching to all the possible name combinations and as it turns out, there are 1,990,114 Total wizard names possible. (side note: it was brought to my attention that this information was also figured out independantly on Wikia even earlier than this.)
. . . thus giving you a 1 in 1,990,114 chance that someone else will have your same name . . . you may fear Julia's number abilities, but do not fear mine.
In addition here, I think you have to consider the "x" factor in names. For instance, if you choose to name your character Patrick Star, Luke Skywalker, or Taylor Swift, I guarantee your chances of running into another wizard with your name will escalate. (AHA! Not as original as you thought you were, were you Mr. name dropper!)
Also, if you're a 1 name person, your chances are also going to escalate (like 1 in 139 as Julia pointed out). I can't tell you how bummed my fire wizard named "Digby" was when he ran into another "Digby" out and about. (Sigh, and I really liked the name Digby--just Digby--too)
I've yet to run into another Thomas Lionblood, Kyle Skystaff, or Amber Deathsong . . . although now that I've posted that, there are now 10 bloggers making characters with those names to torment me with screenshots on their blogs with said names. It's ok, I'll become an action figure for you to model (if only I could convince our friend Terry Dietz to make a Thomas Lionblood figurine).
You know, there might also be some kind of mathematical curve towards wanting to name your character to match your class. Throwing the name Death, or Hex, or Blood into your name as a necromancer is very attractive. You know what I'm talking about? If x=evil name and y=necromancer, then n2 +9 +9 . . . to further understand this, you must watch this presentation on maths.
The British always seem to make me feel more sane.
. . . what? I'm just doing my part to get you guys ready to go back to school . . .
Anyway . . . THAT's what goes into your name combination. Um, Or something like that. I'm not so good at maths, but thanks for the eye opening post on possible name combinations, Julia!