The heartbleed incident does not disprove that 'given enough eyeballs all bugs are shallow'. Instead, it proves the importance of Open Source software. It also illustrates the disadvantage of not having an enormous marketing machine that can spin such incidents. Instead of calling this bug 'catastrophic', we should have called this 'an opportunity to further improve server security'...

Peer review is the quality control...

xxxx Note to self: in future prefix notes to self with an easy to find string such as 'xxx'.

One example of a graphical coding environment I have experience with is LabVIEW. I sometimes use it for simple projects. It is surprisingly easy to create an un-maintainable mess in LabVIEW when things get even slightly complex.
Diagrams need to be translated into words before humans can reason about them; this translation is not needed with written code. Thus written code is more effective to fully define a software program.
This is also the reason that code generation from UML has not caught on in mainstream programming.