I've been reading some of the responses posted here which are pretty good and inspiring.
I just did an exercise on writing my own eulogy that helped me clarify what should be my life's purpose. It might appear morbid to think about death but it really had me thinking about the direction that I want to take. I took more than an hour to compose mine. You can read my eulogy here
My Eulogy Defines My Life’s Purpose » How To Use The Law Of Attraction
Perhaps, those who have been struggling to finding their purpose, can do a similar exercise, provided they feel up to the "spirit" of the exercise. Work backwards from the end in mind to find out what you need to do today.
Hope this helps,
Eve