Suhail, with regard to impact on installed sites I agree that lost event data is not the end of the world. However, it's currently taking 20-30 seconds for requests (inserting the mixpanel js) to timeout. During the outage, it would be much less painful if the requests were failing more immediately.
I just sent this same message to support (at) mixpanel.com.
EDIT: just to reiterate -- the major problem isn't the API being down. It's the extreme timeouts being experienced trying to load a static JS file.