Right, the incoming and the outgoing packets should be logged, that’‘s the idea behind it. If you are using the Content Filter Plugin you’'ll see that this does not work as expected, packets are processed by the Content Filter before the incoming packet is logged.
characters like á, é are not encoded properly
Which program are you using to display the log files? They should be UTF-8 encoded without a BOM-Header, browsers should display them fine.
is it possible to know what files were transferred?
i don’'t think so. The file transfer will be initiated using XMPP packets and these will be logged. One may get some information out of these packets.
I also found something odd. The conversation log is fine when is from an Openfire user to another Openfire user, but when an Openfire user receives an answer from an external user (MSN, for instance), it just logs what the Openfire user typed but not the answer from the external user.