What is the greatest HP prediction ever?

[Neri]

This post 
http://groups.yahoo.com/group/HPforGrownups/message/161571
by Alla in the main list makes me ask: what is the most inspired,
brilliant and exact HP prediction you have ever encountered?

Note: if possible, I'd like to see some substantiated proof: a post in
HPfGU or another public forum with a date earlier than the publication
of the canon in question. 

Neri