Comment 4 for bug 671746

#2 is tree like view of the mails..

+ from A
| + reply to A from B
| | + reply to B from A
| + reply to A from C
| | + reply to C from A
.. and so on

Conversation view is like gmail. Just a single thread of replies to the main mail, arranged in chronological order.

The latter is way moreuser friendly, and a much requested feature in mail readers.

~Anil