AddThis

You're probably viewing your pages by opening them as local files rather than loading them from a web server. So instead of the URL of the page in your browser starting with http:// it starts with C:\ or file://

Here's what the AddThis buttons look like when viewed via http:// - http://i.imgur.com/IDGUD.png

And here's the same file viewed using file:// - http://i.imgur.com/gpCco.png

We currently are using protocol-free URLs in our code - ones that start with // instead of http:// or https:// - to make sure our SSL implementations are cross compatible without extra work. However, if you're loading the test page with the file:// protocol it causes the CSS and other JavaScript files not to load, since it's looking for them on your local machine rather than our web servers.

I've submitted a ticket to our developers to fix this for people previewing pages using their file system rather than a web server, but until they can get that implemented you should either understand that the buttons won't show up if using the file:// protocol or use a web server in order to test how your sites display in browsers.