If you're Ubisoft, you've got expected sales numbers, which makes projecting load levels trivial and easy to plan for. So, the options are:

a) Ubisoft MASSIVELY underestimated the number of sales they'd get (not likely, given AC1's success and Ubisoft's experience)

b) Someone MASSIVELY screwed up the load calculations and wasn't cross-checked (not likely, given what's riding on those servers)

c) They're being DDOSed (very likely, given how easy it is to get ahold of a botnet these days)

Except, every single MMO that has ever come out has had problems in it's early days, despite having pre-orders, betas, and other stepping stones, and the knowledge that every single MMO that has ever come out has had these same problems.

Ubisoft screwed up.

Even if it is a DDOS, they've still screwed up by implementing the system they implemented, which amounts to a single player local game requiring a 'Net connection to play. I was considering buying AC2, especially since I live here in Montreal and would love to support the home team, but I won't. I don't want to buy a game that can't be played, and thats what they are selling. A "Loading" Game.