This doesn't really affect my company much, as we have 5 people of interest - the price is the same. We opted to switch, so that we can keep client code backed up there. Unfortunately, outside collaborators cost money... so keeping clients involved to that degree now costs money. On the plus side - we now have an excuse to keep our repos to ourselves.
Private plans also have infinite repositories - so you can hide your horrible TINS code from the world forever! 
This sits well with me, as I was going to toy with setting up some side projects, and I no longer have to make them public right off the bat. I'm trying to switch us over to making 'trash' branches that just get merged into master - we've been doing it the other way around: master is garbage, there's a production branch...
rant over.
I've always preferred Bitbucket's model of per-seat pricing. Good to see GitHub joining the club of sanity.
The reality is that more active users === more system impact. Having hundreds of rarely used repositories barely costs them a dime (in storage).
This sits well with me, as I was going to toy with setting up some side projects, and I no longer have to make them public right off the bat.
By the way, you can have unlimited, free private repositories at Bitbucket if your team size is no more than five people.
Open source is the reason I started to look at git and github.
still learing.......