@johnccr asks me to give a look to the new OWASP Top Ten 2010 RC1 (pdf), saying "it would be interesting to know if it changed your perception". So here are a few quick comments.
I'm certainly happy to acknowledge that this version makes the limitations of the Top Ten approach much clearer than previous versions, and explicitly encourages organizations to "think beyond the ten risks here". The document is careful not to claim the Top Ten as a full application security program, and warns readers not to stop at ten, because "there are hundreds of issues that could affect the overall security of a web application". But then surely this implies we shouldn't be wasting time reading this document at all; we should be reading the OWASP Developer’s Guide, "which is essential reading for anyone developing web applications today".
The status of the top ten items as risks (rather than, say, weaknesses or vulnerabilities or threats) is also a bit clearer, and the ranking of risks is based on the scale of the risk, not just the frequency of the attack. However, the document also refers to "relatively simple security problems like those in the OWASP Top 10" - which makes it seem that they may be the most obvious rather than the most problematic. Making people aware of simple problems doesn't necessarily promote awareness of more complex problems.
To my mind, the trouble with this kind of list is that it encourages bad thinking. Not only are some risks regarded as more attention-worthy than others (based on a generalized model of risk that may not be relevant to your organization or application portfolio), but each risk is considered in isolation. But a holistic understanding of security and risk needs to look at the composition of risk - how can several apparently small risks sometimes be multiplied into a very large risk.
I'm also concerned about limiting the analysis of risks to application security itself. Presumably a full security risk analysis would need to look at social attacks as well as technical attacks, but the Top Ten are all drawn from the technical side. I looked for this technical focus to be stated and explained somewhere, perhaps in a statement of scope, but couldn't find anything to this effect.
By the way, when I have raised issues about OWASP in the past, I have been challenged to fix them myself. But I'm not a normal member of OWASP, I'm an independent industry analyst who has been asked by a few OWASP members to provide coverage of OWASP. I am happy to enter into further discussions with OWASP members, but if you want me to build stuff then I am going to have to find a way of funding my time.