[xxpor]

>But if you can continuously update the live site its not that big of a deal if a bug gets out. It will be noticed soon, often by your users, and then you fix it and that is it.

You consider this acceptable? "Don't worry, if there's a bug, our users will tell us, no need to test!"

[shpiel]

Yes. Not all bugs are the same in terms of end-user impact and how they affect the overall performance of the system. You can expend a lot of resources trying to track down every single last glitch in many cases you should. However, if you have the luxury to be able to push updates and fixes at any time and you a free non-critical service, its better to just have a culture of fixing things quickly and allocating resources to more high-priority things like adding new features.

More eloquently stated: http://www.quora.com/Quality-Assurance-QA/When-is-not-having...

Ideally, most of the testing should be automated and engineers should be writing test cases as they build features.