PugsAce: I s'pose quoting oneself doesn't count? :)
Yes, it does.
PugsAce: but starting a new thread doesn't!
Yes, it does.
PugsAce: And editing counts, too!
No, it doesn't.
PugsAce: But only the first edit?....
Nope, none of the later edits counts.
What's really happening (or rather, isn't happening), PugsAce, is that your post count is not being updated in real time. So, your post count may say 99, you post 3 times, and your post count will still only say 99... But then, 5 minutes later, it might jump from 99 straight to 102 so that the sum total is correct.
As to what achieving 100 posts signifies, it's that your real life is in danger of becoming overshadowed by your virtual life. That may or may not be a good/safe thing, depending on your preference.