In my final months at Microsoft in '97, I tried (but ultimately failed) to convince the messenger group to acquire Mirabilis, a small Israeli software company behind the instant-messaging client ICQ. ICQ was acquired the following year by AOL for around $200 million.
Today, I look at the dramatic rise of FriendFeed, a clever nexus-of-social-networking. They are developing a pretty valuable "traffic cop and more" foothold amongst people, and may someday soon hold richer "social graph" information than even Facebook. Check it out soon, Microsoft!