iChat is not the only IM client for mac, but it's well integrated with the OS, so I always wanted to throw away msn messenger (which i've been used for longer) and pass all my old contacts to ichat. I found this blog post which was very very useful in describing how to set up a jabber account which connects to an msn one, and then add the jabber account to the iChat client. Easy!

From the same blog, also an interesting tutorial on how to tag photos using iPhotos (did u know you could do it?)