Here at CNET.co.uk, we use Yahoo Messenger a lot. Because we're all gigantic geeks we very rarely actually talk to each other, instead preferring to type our messages using l33t speak via IM. YIM wasn't my choice -- I much prefer MSN -- but everyone else was on Yahoo when I got here and while the two clients can talk to each other these days, you do lose some functionality going between the two.
So Yahoo it is. But there is a fatal flaw in the version I'm using. When I open the main messenger window to IM someone, I've noticed that sometimes the person I double click isn't the person who actually gets the message.
The consequences of this range from the mildly irritating -- sending an amusing link to someone who doesn't care for amusing links, say, the MD of the company -- to the utterly dire, which I'll illustrate below:
It goes without saying: I'm very careful to check the name on the window when it opens now.