The 451 Group's latest venture capital report shows open source funding taking a 12-percent slide in Q3 2008.

The 451 Group's Matt Aslett offers several explanations, but here's one that he missed:
Perhaps the data was faulty.
The report leaves out a range of companies that are open source but don't appear to have made it into The 451 Group's calculations. Some of these investments simply haven't been announced yet (I know of several), while others (like CloudEra) have, but don't seem to have made it into the data.
It's hard to tell since the report doesn't list the deals, but it does mention that there were only two Seed or Series A-stage deals. This is simply not true, but it's not really The 451 Group's fault: it was simply relying on publicly available data.
I have no doubt that open-source funding is down, or will be, but until we have an accurate data set, it's hard to draw too many conclusions as to how deep it will be and for how long.