Gmail pulled a fail whale and a number of people are talking about how their productivity was damaged. Systems are going to go down, it's a fact of life. What's important is to be prepared when those systems go down which is a major reason that some kind of offline access should be built into systems like email. In theory we'll reach a time when the cloud really is always on, but we're not close and it may never happen.
When a company like Google, which has a ton of redundancy built in, or Amazon S3, has issues, we've got to have applications and systems that let us continue to work. And Google has a built-in solution for people with Gears. So why haven't they rolled it out yet? Because synchronization is a really, really hard problem. And I think that problem is what prevents a lot of services like Gmail like incorporating offline functionality. The web needs to focus on solving synchronization so that outages like these don't have to affect productivity like they do currently.