One of the toughest things about a big corporate job is the big corporate firewall. Although many companies have good intentions, the average employee can get cut off from most of the internet - at least the most interesting parts of it.
Fortunately, there are a number of web-based applications that help you get around these limitations. Meebo certainly works towards negating the IM wars between AOL, Yahoo, MSN, and GMail/Jabber. Through the magic of AJAX, you can talk to anyone in any of these applications through a single internet window. And since you don't have to download and install any programs, it is very firewall friendly.
Meebo can also be set as an active-desktop. In other words, a Meebo session can replace your desktop image and you can IM your friends without opening a window.