Disclaimer: I haven't used Windows 7 for more than a few hours in a VM.
That said, as I understand the technology:
VHD is already use in VirtualBox. It's just a file format for your hard disk images. Windows 7 adds one big feature that Linux doesn't have (that I know of)--without modifying your MBR, it lets you boot off of a VHD. So let's say you've got Windows 7 as your only OS, but you've been messing around with Ubuntu 9.10 in a VM. You can boot from the VHD, and it works like a normal OS instead of running in a window. It saves you repartitioning, installing Ubuntu from scratch on the new partition, reinstalling your programs, and migrating your settings. Windows 7 can also mount VHDs, which is a nicer way to move files between the guest and host.
You should read the wiki on BitLocker before you make a purchasing decision based on it. I personally prefer the way TrueCrypt does things, but if you've decided to go with full disk encryption, BitLocker is going to be one of the more transparent options available. You're limited to 128bit AES, though--no choosing your key strength or chaining algorithms.
I'm very happy with Arch Linux, but if I were buying Windows 7 and paying for it with my own money, I'd go with Home Premium. The only tempting features in Pro are the RDH and XP mode, both of which I can easily replace with freeware. If my company were paying, Pro.