There aren't really any obvious business lessons to learn from this that I can see. The growth is largely down to word of mouth (they have an evangelical fan base after all) and the site was set up with empathetic money from the church or otherwise.
Well, the hype is up now. People are probabaly already going to the site.
All it takes is a few priests and/or evangelists to drop the name a few times (you can see our sermon on GodTube.com, check out GodTube.com) and it's wildfire. This is 100% free advertising on a massive side.
I was raised Catholic and when I got older (including recent masses for family events (weddings, christenings etc..) I paid more attention to what they priests were saying during their sermon and they must have a PhD in name dropping. They can drop a name in almost any speech and most listeners won't even pick up on it. Mention it a few times and people will remember it and possibly migrate over to it.
Christians are very loyal, too (for the most part). Once "GodTube" is in their minds, they'll remember it (bookmark etc..) and link to it thus ranking the site higher.
I think there is some business lessons to be taught here.