Through no fault of the Ohloh tool itself - it can only report on what it's told, after all - the reports that Ohloh generates should not be considered The Gospel.

He gives the example of the PHPSurveyor project (a lesser known project, at least to him) and ran the numbers. They came out with a surprising "731,822 lines of code, and would cost approximately $11 million dollars to reproduce".

Digging down a bit further, it looks like Ohloh is looking at the complete SVN repository for the project (both stable and development). Clay compares the two sides and finds only around 195,000 lines of code to Ohloh's findings of 731,822.