So I have just read this link and it made me think: There are so many factors to consider to create a reasonably safe bitcoin client that there ought to be a flawed and exploitable client sooner or later.
So, has someone evaluated the security of the most used clients (Satoshi, Electrum, Armory, blockchain-info, ...) so it's safe to assume that the generated private keys are unguessable? I'm talking about weak RNGs, reused random numbers and the like. Unfortunately I know way to little about cryptography to do it myself.

Also it would be useful if someone with more grasp of the concept could create a checklist of possible vulnerabilities to avoid when coding a bitcoin client.