Despite the uncomplicated version number, open-source, multiclient chat app Pidgin 2.5 doesn't include any major improvements unless you're fascinated by bug-fixes or are a big MSN-messenger user.
Available for Windows, in a portable version, and for Linux, the update features support for Microsoft's Live Messenger offline messaging, and personal messages. The latter will show up as Status messages. Live Messenger's non-face Smileys should be updated, too.
Other improvements are much smaller in scale: Group and Chat buddy list entries now support custom buddy icons via the context menu, and there's the usual spate of stability improvements across the board. I had noticed some stability issues with Yahoo IM in the previous release, version 2.4.3, and so hopefully those have been resolved, too.