LiveMessage – 10,000 Beta Bloggers in the First Week
To see how it works, you need to have Microsoft Messenger running on your computer. Go to a site running LiveMessage and click on the appropriate link (e.g. Bink.nu has a LiveMessage button, Flexbeta has a Flexbeta Alerts button, Feld Thoughts has a LiveMessage button, and OnlyOnce has a LiveMessage button.)
If you have a blog consider trying out the LiveMessage Blogger alert service as an option for your blog subscribers.