Capitalization

My mom was delighted when her great-uncle, Great-Uncle Sam, came to visit.

Great-Uncle Sam hadn't seen Mom in nearly two years.

He was busy being President Uley.

If the person's name would make sense in place of the word, then capitalize it. For example:

"Yesterday, Dad bought a new shirt."
"Yesterday, Alan bought a new shirt."

But not,
"Yesterday, my Dad bought a new shirt."
Because there is no sense - at least not in the same way as the first one - in writing:
"Yesterday, my Alan bought a new shirt."
Instead, that example should be written:
"Yesterday, my dad bought a new shirt."

That part is easy enough.
Now, we move on to titles.

You wouldn't write mr. Hathaway, so why would you write president Bush?
President in the example above is just as much a title as Mister.
When president serves as just a noun, and not a title it will not be capitalized:

"President George W. Bush has been the president for eight years."

What about when a person doesn't use the president's name and just calls him or her by the name President?
Since a president is a person of authority it is bad etiquette to just refer to him or her by the term President, alone. However, the terms Mister President and Madam President are completely acceptable.