I've had an issue for the past few months, but I rarely restart so it hasn't caused too much trouble.
Basically, when I start up my Mac (iMac10,1 - 3.06GHz Intel Core 2 Duo, OS X 10.6.3) everything proceeds as usual until I reach the login window.
The login window displays normally, but keyboard and mouse input seem to be ignored. This condition persists for around 5 minutes at which time everything goes back to normal.
While the login window is frozen my second monitor appears entirely blue, the second monitor receives a background as soon as the login window becomes responsive.
If I startup while holding SHIFT the problem still occurs, but the freeze is much shorter.
Looking through my logs I see no activity during the time that the login window is frozen.
I've attempted to repair disk permissions, and gone through every possible maintenance option in Cocktail.