One nice feature about WHS is it's ability to efficiently backup all xp / MCE / Vista pcs on the LAN. It does this by storing a cluster of data once, and putting a database entry of that cluster and which PC it came from (non techno description). It will do same for all PCs. Then, if the clusters are same, it will only store it once, and put two pointers in the database.
Example of it's use: On those LAN PCs, one of the common apps might be MainLobby. This might be 10 - 60 gig of "stuff". The files that may be different from PC to PC might be a meg or two. To backup all of the PCs running MainLobby, you are only backing up MainLobby "once", with a relatively few clusters that are unique from PC to PC. So, if you are running 5 PCs running MainLobby client, you only need the backup space for one to backup all 5.
With RAID, this is not how it's done. You would be cloning or imaging or file copying each PC individually, and then storing that image across multiple drives and a drive or two more for backup protection of the hardware. ie: use more space.
The other thing is that these backups occur automagically. Now, if you are good with software selection, installation and configuring (and do it), this is no great feat....but for the rest of the world, this is important stuff to keep running trouble free.
Also, PCs are becoming our media central. Single source storage of those big ole files is important for saving money, and saving sanity by decreasing complexity. WHS provides an easy to configure means to share content to who you want to share it with. Again, "easy" stuff for techno wizards, but "hard" stuff for everyone else.
I am really impressed with the quality of the installation of WHS. Definately the easiest installs I have done. And, setting up the other PCs on the LAN to do the above is equally easy.
What I don't like about WHS is Microsoft's very limited view of what WHS is for. Their discussions talk about how nice WHS will be for "Home Automation" et al, but their certification process for OEM's is completely counter productive for those purposes. ie: limits on serial ports and other I/O stuff, adding custom shared folders in an initial build, etc. Funky stuff for an automation controller.
What I really like about WHS, is even though their Certification process doesn't support HA, their software does just fine. MainLobby / MainLobby Server runs on it very nicely, and that is the most important part for us