I've seen the whole thing a few times, definitely an awesome video!
Anthill (the filmmakers) has put almost the entire thing on Youtube, segment by segment, over the last few months. I'm sure the last segment or two will be up sooner than later.
I bought "Follow Me" (the previous film from Anthill) on iTunes when it came out, and even though it's supposed to be in HD, it doesn't look that great. I think the Youtube 1080 quality of the Strength In Numbers clips is higher than my Follow Me itunes copy.
If I were to purchase SIN, I'd probably buy it on Bluray, but not everyone has a BR player.
I got to go for a week in Whistler and was fortunate enough to go to Summer Gravity Camp (awesome birthday present from the wife). I hadn't seen this movie yet, but watched it the fourth day I was there when the coach/guide (some guy named Adam) mentioned he had a "small" part in it. Kind of embarrassing, but man oh man can that guy ride. Claire Buchar is in that segment too and was my coach at SGC for a couple days - totally amazing, fantastic coach and wicked fast as well. I got to follow Chris Kovaric down Blue Velvet and Black Velvet and was riding behind him when he did one of those power slides like he did in the film segment – he held it for like 30 yards down a scree field at full speed - mind blowing...