Don't even get me started on the mac client... constantly drops calls, other end complains that sound quality is terrible despite high quality headphones, screen sharing stops suddenly mid presentation, can't see scheduled meeting directly in app, and overall horrible UX.
Also, despite the rigid security policy where I work, the mac client stores my password in the keychain.
But, the boss will see when you're "available" straight from Outlook, which is where he lives. It's not an IM tool, it's (yet another) instrument of workforce control.