Hyper-V Server 2008 R2 will have one ability not found in any edition of Windows - it will be able to boot from flash media.
While this doesn't mean much now, in long run OEMs will start selling servers with Hyper-V already inside. It seems to me that it will be very hard to get server without it. It will be free for OEM and I can imagine quite a few customers actually sticking with it.
Hopefully we are not too far from day when Windows will boot from USB.
P.S. This seems to me as attack toward embedded VMware ESXi. Critics would say that Microsoft waited for cheap 32 GB flash modules. :)