I've noticed that with my MacBook Pro late 2008 (unibody) connected in closed-clamshell mode to a 20" Apple Cinema Display, wake from sleep is significantly slower than in 10.5.5.
What I've noticed is that upon waking, the backlight comes on (the screen is blank), then there's a slight delay, the display shows everything as it was before sleep, then it flashes blue (my background color) and refreshes, showing what I just saw. It's basically doing the same thing twice -- I guess it's being very sure to check to see whether a display was connected during sleep. There also wasn't the wakeup stage where the screen is dark but the backlight is obviously on.
Anyone else?