I've tried to like Messenger:mac, but it just can't compare to the customizability of Adium. Also, Messenger doesn't show the contact pictures, which is a huge negative for me. If Messenger could at least be updated to support audio and video, and allow for some customization, it would definitely be a great IM client. Most of my contacts are on Windows PCs using Windows Live Messenger, so the ability to add other IM accounts isn't a big deal for me. It really amazes me that the Mac BU at Microsoft hasn't updated Messenger:mac yet to support the same feature set as the Windows version.