Time Machine was one of the key features introduced in October 2007 with OS 10.5 Leopard. Of course, Apple had problems getting its own Airport Disk to work with Time Machine; let's hope HP has made a better first attempt.
HP's MediaSmart Servers run Microsoft's Windows Home Server operating system. The internals of the new ex485 (750GB) / ex487 (1.5TB) have been upgraded to Intel Celeron 2.0GHz CPUs and 2GB of DDR2 RAM from HP's original ex470 (500GB) /ex475 (1.5TB), which had AMD Sempron 1.8GHz CPUs and 512MB of RAM.
Compared to ordinary NAS devices which simply add storage to your network, these HP Servers come at a premium, there's no doubt about that. The ex485 is $599 and the ex487 is $749. In other words, you pay for all the functionality that you could, in fact, perform manually (or have other software perform automatically, rather than the server software).
In addition to Time Machine functionality, HP has also teamed with Amazon to provide an Amazon S3 managed online backup service. Of course, you could easily use a service like Mozy for your PCs, but most of those services don't work with NAS.
However, this is another way to suck the life out of any broadband caps you may (or may not) run up against.
HP has also added a free 5-year SSL certificate when you activate the remote access using the HP Personal option, eliminating the warning messages you used to see in your browser.
Finally, another feature of MediaSmart is remote MP3 streaming. However, when streaming over the web, the software transcodes MP3s at a 128kbps bitrate, to minimize any potential for choppiness.
BTW, if you run over to HP's site and check out their whitepapers, you might get confused. They haven't updated them and the information (like no Time Machine support) is old.
Features of note in the HP press release: