I ran into a strange bug with pidgin where I could not log into Yahoo. Strace did not shed any light on the problem:

gettimeofday({1245688276, 23774}, NULL) = 0
open("/home/alan/.gnome2/nautilus-sendto/spool", O_RDONLY...
fstat64(7, {st_mode=S_IFDIR|0755, st_size=4096, ...
getdents(7, /* 3 entries */, 4096)      = 48
getdents(7, /* 0 entries */, 4096)      = 0
close(7)                                = 0
read(3, 0x93c4508, 4096)                = -1 EAGAIN ...
gettimeofday({1245688276, 24697}, NULL) = 0
poll([{fd=4, events=POLLIN}, {fd=3, events=POLLIN},...

Instead, the answer came from a blog post here.

Yahoo changed their login protocol. Pidgin released an update. Ubuntu did not propagate the fix, apparently because it was not a security bug, but new functionality.

The pidgin developers have released an Ubuntu package in their PPA (Personal Package Archive). See the details at the pidgin web site here.