Gmail and for Gtalk.
Outages like this in my company are a big deal. Although we have our phone systems and email servers setup and actively running, the main form of communication the majority of of us have between our many offices is through use of GoogleTalk. Today, we're thinking of how bad of a business plan it is to have our main form of communication a free 3rd-party service, but considering Google's track record you wouldn't normally have Google downtime as your top concern.
Unfortunately for me, 30% of my Googletalk work contacts have email addresses that i know they actively check for work related emails, and of those only 15% have extensions i can directly reach them at.
Our reliance on the Cloud is expected as the convenience for it's use for the general public's shortsighted wants and needs outweighs the potential for disaster that may occur in the long run, but today...i just wish i had thought to get secondary contact information for some of the people i need to work with today!