Well 5 Months later, and the 550 has caused more consternation.

Come home from mothers day brunch to find the 550 in Xbox Media Center activity. I press activities - nothing happens.
Cycle power - unit boots normally. Except refuses to obey any button push. No change to LCD at all, and never transmits anything.
Swap batteries - nothing
Cycle power & hold down 2 key. - nothing
Fire up pc & update remote via Logitech site - nothing
Cycle power & hold down 2 key - nothing.
Put remote in freezer.
Call wife ask her to pick up alkalines on way home
After finally finding remote - put alkalines in cold remote - nothing.

Arrrghhh!

THWACK! = Me banging remote on coffee table for a little kinetic fine adjustment.

Lo and behold, remote is back to it's normal self.

Think I'll pick up a spare.