This is why on Indefero I offer only a limited space free account (still with your own domain). The percentage of people using for free such large offers is too high. This is because you are dealing with people who know how to integrate with different services (googlegroups, wikispace, sourceforge, etc.) and can get a really nice setup for free.

From a business point of view, I definitely prefer to have less visibility but a higher percentage of paid customers. This allows me to create a product which is of high quality on the long term because I have money to do so. And in fact, discussing with my customers, they prefer it that way.

Note that the free offer of Assembla is not free, you get direct advertising when accessing your space.

But if we do small maths and we consider that Assembla has the incredible 5% conversion rate from free to paid. This means that on average they will have for 100 users:

95 x 1GB of "free data" 5 x $49 x 2.5GB of paid data

I take the 50% usage as on the long run it what my personal stats gives me.

So about 100GB of data for $245 per month. As you need a triple backup to be robust. It means 300GB of data to maintain for $245 per month.

It is possible, but the margin will be razor thin if you want to provide quality. It is a bold move, I am eager to see how it develops.