I just upgraded to the last version of adium, to notice that
all of a sudden my yahoo connection fails. After a bit of
tweaking (and motivated by the fact that one of the new
improved "features" is related to the way that passwords
are stored locally), I decided to change my yahoo password.
Everything worked ok after.
The older yahoo password included some funny characters (i.e. ~),
and I am thinking, maybe it has to do with the way you encode
the passwords locally that might be the problem.