I am pretty sure that none of the currently available HD DVD titles use the network for anything, but wanted to double check.

Are there any announcements of discs that will take advantage of this feature (and how)?

-Pablo

Blood diamond. It gives you a map of stores near you that sell the popular items. Or something like that.

But, yeah Blood Diamond.

Bandai's first release is also supposed to have network capabilities:

http://www.avsforum.com/avs-vb/showthread.php?t=822205

The “Freedom” HD DVD/DVD Twin disc will also include HDi (*2) network function which will offer new ways to enjoy the product."