useful for something - aspirin is useful for headaches
useful for doing something - aspirin is useful for getting rid of headaches
useful for someone - It would be useful for us to find out what his plans are
useful to someone - His plans were useful to me
I'm not immediately sure if there's any difference in sense between:
'useful to somebody' and 'useful for somebody'
and yet in the above 2 sentences I would prefer 'for' in the 1st and 'to' in the 2nd. Thoughts anybody?