Sunday afternoon saw the customer-facing side of Yahoo's email systems go down. While email was being accepted in, POP and web access to mailboxes was very flaky until mid-evening. Even then, it came back in dribs and drabs with some email accounts getting POP access hours before others.
In the Web 2.0 mashup world, many of the participants offer services that are permanent beta, and come with few service level guarantees. Resilient data centres don't come cheap (or grow on trees).
You get what you pay for.
Yet you also come to rely on what you can get.
The Rupert Murdoch-owned MySpace community will be shaken and weakened by this prolonged outage. The only plus side is that they'll have had no where to vent their frustration as their blogs were down!