Salesforce was down for a long time a couple of days ago - but nowhere near enough time to jeopardize the promise of 99% uptime. Actually 99% isn't that good - it's 3.65 24hr days of downtime every year (so 7 hours every month). 99.9% is still 9 hours a year and assuming scheduled nighttime downtime is not part of the guarantee Salesforce could still be within 99.9%. Real guarantees of "never down" et the experience level start at 99.99% uptime - which is 50 minute downtime and the legendary 5 nines is "unnoticable downtime" I doubt very much that any company with any kind of complexity in their offering offers this. Amazon doesn't. Google doesn't, probably banks would like to say they do - but mine certainly doesn't.
It's an unforgiving world where 2 nines is a news story.

(incidentally, salesforce.com is the only website I have ever seen where you had to sign up to access flash-based ads for the product)