It had been a long time since I had used Yahoo Messenger; however, I needed to install it and use it the other day, after doing so I found something which I found cool enough to blog about: Yahoo Ping Box!
With a couple clicks I was able to embed a yahoo messenger client right inside my blog. Or on any of my other sites / social networks. It was even easier then setting up AdSense. When you enter a nickname, my yahoo client is notified that so and so user has logged in. This is a negative in my opinion, as it pops up a little toast and it doesn't indicate it's from an anonymous source.
However it does warn you when you have an open chat window that it is from an anonymous pingbox user.