hate the Microsoft MSN client with lame adds and that popup at the start with a timeout.
Same counts for ICQ and AIM.
But that is not half as bad as installing stuff all over the place (there is an expert mode to YIM that won't do that I'd hope (I'm not even going to reboot to win for this))
Well... ads are something which may be a concern.. but they have to do it.... to make up for their revenues...

They put various stuff all around the system only for a purpose .... of course if so many features are to be bundled together with the IM then the system has to be fine tuned at various places.. Thank god the installers do it automatically....