I have been using Yahoo messenger for over two years.
I love its smileys and use them liberally in my chats. I find it most convenient to chat on yahoo and most of my friends/relatives contact me on yahoo. I have been able to cut down on my telephone calls since I started using yahoo.
However, in the last couple of months, when I tried to log in, I have been experiencing difficulties. Don’t know - probably they are upgrading their servers! Of late, I discovered downloadable musical rings for my cellphone on yahoo.
If your computer has cable modem/high connectivity, go for Yahoo, otherwise on dial-up connections, sometimes you get problems.