If you press Windows + C in Windows 8, you will get the new UI element called the Charms Bar. It contains some useful links for sharing and searching:
If you want to customize it, searching on internet will probably lead you to a third-party application like this or this. However, it seems that they will only allow you to set a new skin for the bar's buttons.
Is it actually possible to add a new button or remove any existing button from the Windows 8 Charms Bar?