One of the innovative things I like in Windows Home Server is its "infinite storage pool" idea. If you run out of disk space, just add water. Errr... just add another hard disk :-) be it external or internal. It's that simple. When you add a new harddisk, no need to initialize disks, create partitions, volumes, etc. You don't even have to know about this stuff.

And if one of your harddisk fails, your data is still safe - every file is stored in two separate copies on two separate disks.

Another thing I like is that the server doesn't even have a monitor. Yes, you don't need a monitor for a Linksys router - why would you need one for your storage server?

More details here: http://www.stopdigitalamnesia.com