Oh really??
Initially, they were worth exactly nothing, they could have said 999,999,900% and still be technically correct.
Perhaps it is more accurate to say initially they were worth an unknown amount. The first transaction assigned a value to them, and then you can measure from there.
I think the value first given to bitcoins is described on this page: http://newlibertystandard.wetpaint.com/page/2009+Exchange+Rate
From that page: "During 2009 my exchange rate was calculated by dividing $1.00 by the average amount of electricity required to run a computer with high CPU for a year, 1331.5 kWh, multiplied by the the average residential cost of electricity in the United States for the previous year, $0.1136, divided by 12 months divided by the number of bitcoins generated by my computer over the past 30 days."
Good find!