My team has a goal of 110% automation, but: not every test is worth automating. What's more, the value in automating a particular test case changes depending where in the product cycle you are. Or as I said in a presentation on this topic:
What should you automate? Everything!
What should you automate when you are three months from shipping? Much less!
How do you choose? When it comes right down to it you have to make a judgement call. But there are some guidelines that will help you decide:
"I don't believe you - of all people - are really saying this!" I am most definitely not saying that 110% automation is not a worthy goal. Having every last test case automated would vastly increase your confidence in your application, and it would really pay off come sustained engineering time. But you know as well as I do that there's never enough time to do as much testing as we would really like, and so we have to prioritize. Deciding what tests to execute manually rather than to automate is just as important as deciding what tests to do in the first place.
Having trouble prioritizing? Try this: If you could only run ten automated tests - and not do any manual testing - what would you automate?
*** Want a fun job on a great team? I need a tester! Interested? Let's talk: Michael dot J dot Hunter at microsoft dot com. Great coding skills required.