Well... you are somehow right...
After having re-built my extension caches (they really needed it) yesterday, I tested various patterns of shutdowns/reboots/iTunes launches, and never experienced the freeze anymore.
But your message made me doubt, so I tested again.
And I got those freezes again, yet in a less "reliable" way than just after having applied the 10.6.7 update: currently, iTunes sometimes launches without a glitch, and sometimes provokes the freeze, without a really discernible pattern.
As a result, I won't dare launch iTunes without being sure to have a ssh access to my box (yes, a clean shutdown is still possible thru ssh) until a true explanation/fix has been provided...
My apologies for having been too optimistic,
Axel