I don't think I've ever used the Caps Lock key - all it's ever done for me is cause pain and grief and wrong passwords or inadvertent 'shouting' in e-mails. It's a fossil from days gone by.
Go into System Preferences, select the 'Keyboard and Mouse' or 'Keyboard' panel, click 'Modified keys...'
and set the Caps Lock key to 'No Action'.
Takes all of 10 seconds!
Cheers,
Kris