Boyhood is quite unlike any film I've ever seen. If you've seen it, you're no doubt a little bit obsessed and want to know more about it. A good place to start is with the Boyhood FAQ, but it's also well worth having a dig through this lot:

Reviews from all the usual respected sources: Adam Batty at Hope Lies; Ed Williamson at The Shiznit; Neil Alcock at the Incredible Suit; Liz Beardsmith at Empire; and Mark Kermode at The Guardian.
Linklater discussing the making of the film on Film4.
Drew McWeeny and Ali Gray both give personal accounts of what the film meant to them as fathers (both of which I concur with – it's definitely changed how I think about what's to come in my boy's life).
Linklater discusses plans for Criterion release of the film.
One of the many ways the films marks the passing of time is through a rather fantastic of-the-time(s) soundtrack. The dated opening track alone says a lot about how long this project has been in the works. Here's a complete list of every song used. Any film that takes a moment to discuss I Hate It Here by Wilco is okay by me.
Tracklisting for the Black Album.
Linklater and Hawke interviewed by Esquire.
Daily Beast interview with Alabama Worley herself, Patricia Arquette.
The New York Times have a fascinating slideshow of star Ellar Coltrane at various ages. In summary: cute, cute, cute and … BLAMMO! puberty.
As unique as Boyhood is, characters/actors growing up on screen happens on televisions all the time. For example, there's definitely an interesting film to be cut together just using scenes of Sally Draper/Kiernan Shipka in Mad Men (ideally to feature a present-day final scene starring Kathleen Turner … but I digress).
And for some good old-fashioned reading on paper, I can highly recommend Spike, Mike, Slackers and Dykes, John Pierson's account of the American indie scene from which Linklater et al sprung.