ORDER BY id DESC - facebook style? Speed of execution?

Databases
1

The status in the walls of Facebook appear in descending order by the time of status creation.
Since they have millions of such status from all the users, how do they manage this?

ORDER BY id DESC

or

ORDER BY comment_timestamp DESC

would be too poor idea in terms of performance, speed and number of data.

Do you have any idea on how does Facebook manage this?
What would you do if you were to design a such system for yourself?

2

Really? With an index on the ‘id’ or ‘comment_timestamp’ column it should work quite well, shouldn’t it?