Isn't their acrued "debt" actually 20% of what has been paid in? That's about 48 bitcoins as of now.

(Or perhaps that's what you meant?)

Hm, you might actually be right.

I am not sure what the balance actually represents.

There is some list of unpaid 'investors'.

If they are operating as they say, the balance should always be less than 1.2 times the amount put in by the first entry on that list (or so, they could be combining payments or what not).

Remember that it takes a while for transactions to complete, so the balance could be a simple counter of outstanding outgoing transactions.