If you have Netflix you can watch it instantly on your computer. Don't read anything about the film before you see it, the less you know the better the watching experience.
A few Netflix member reviews that say it better than I can:
This film ripped out my heart, jumped up and down on it and then put it back together and left me with hope.
This is perhaps the most moving tribute to a number of legacies of love I have ever seen. I've never ridden such an emotional roller coaster by watching a movie until seeing Dear Zachary
No matter how tough you may think you are, this movie will sit with you for some time.
Most powerful movie I've ever seen...a documentary that will leave you heartbroken. Unforgettable and beautiful.