Has there been a public, in-depth, 3rd party review of the standard bitcoin client? I have experience with software engineering... an industry average is at least 1 bug per 1000 lines of code. The bugs might be trivial or critical, easy to spot or hard to discern or activate. I am NOT saying that the people who write bad code, but that programs are written by humans, and even the best of us make mistakes.
Talk to the people at Conformal Systems.
They wrote a reimplementation of the client in another programming language, so had to go through the code with a fine toothed comb to be able to discover and document all its quirks.