Oracle: Interesting study about count(*) function in Oracle DB

What is the fastest way to count records in a table ?

Or how fast can you find if a table is empty or not ?

I came across this in Tom Kyte's blog.
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1156159920245

Happy reading :-)