Email is an essential part of day to day business -- but it's one of those things you don't think about until it's not there anymore. Google has been trying hard to squeeze their way into the enterprise market with Google Apps, but outages definitely don't help.
Yesterday the Gmail interface went down for almost 2 hours. That includes both personal Gmail accounts, and business accounts that use Google Apps. Apparently, Google has already taken steps to prevent this from happening again in the future -- but isn't that what they said last time?
we had slightly underestimated the load which some recent changes (ironically, some designed to improve service availability) placed on the request routers — servers which direct web queries to the appropriate Gmail server for response. At about 12:30 pm Pacific a few of the request routers became overloaded and in effect told the rest of the system "stop sending us traffic, we're too slow!". This transferred the load onto the remaining request routers, causing a few more of them to also become overloaded, and within minutes nearly all of the request routers were overloaded. As a result, people couldn't access Gmail via the web interface because their requests couldn't be routed to a Gmail server.
Even though they did their best to figure out what the issue was, and quickly fixed the underlying problems regarding this incident, massive outages like this one are a tough pill to swallow. Not being able to conduct day-to-day business for two hours would leave a bitter taste in anyone's mouth.
If there is anything good to take away from this (which is also the reason using Google Apps still makes a lot of sense) it's that Google takes care of fixing everything for you, for free. Your own systems that are internally hosted can fail too -- but if you don't know what you're doing, good luck.