I kinda use aim got me a screen name in the dorms at college to keep up with my friends im "on-line" all the time but hardly ever actually on it, well more so now that is cold and i cant go fishin
I use it for work so I can't really give it out but if you're running more than one account(AIM, Yahoo, MSN, ICQ) you might want to try Trillian. You can run all at once and you don't get all the ads.
Yes Lots of money, but it's perfect for the plane and commute folks! Back when I was traveling, I had an IBM laptop that was pretty large. I really only used it in the hotel room, but lugging it up to the top floor along with my stuff, just to check company email and fill out my time, sucked!