From my own experience running a software development shop, I find that I take often copy my data to external disks. Every once in a while I update an external disk for off-site backup. But now I have five of these disks with multiple copies of the same data. So, having a single box with all that data is really nice. And knowing that one disk is backed up to another is even better. And if I still want an off-site copy, I can plug in an external disk when I choose or store data in the cloud from Windows Home Server 2011. (Note: When I merged all those disks into the disk that came with Windows Home Server 2011, I needed to deduplicate at the same time. Easy Duplicate Finder, from the company of the same name, was cheap and worked perfectly, saving hundreds of gigabytes of space.)
But the Windows Home Server 2011 is not just a NAS box. It also can connect with your client systems through a simple Launchpad download that lets users log in and access different aspects of Windows Home Server 2011, based on the permissions assigned. This is different from Microsoft Small Business Server (SBS), which provides identity management services through Active Directory, as Windows Home Server doesn't use Active Directory. In addition, Windows Home Server 2011 doesn't include Exchange or SharePoint, but then again neither does SBS Essentials because in both cases, Microsoft hopes that you will use the forthcoming Office 365.
Some of the small business value to using Windows Home Server 2011 is that once you install the client connection software it immediately enables automatic backup, so the users' PCs are backed up nightly. It also monitors the health of client systems, so a novice or hobbyist admin can quickly see if users' PCs have the latest updates, are protected by antivirus software, and have been backed up. And it lets you configure remote administration of your clients from anywhere.
Obviously if you need to go beyond 10 users, you want to look at SBS 2011. SBS also makes more sense if you need a higher performance server: Windows Home Server 2011 can support one CPU socket with 8GB of RAM, whereas SBS Essentials supports two CPU sockets with 32GB of RAM and again, it is a domain controller with a 25 seat limitation. SBS Standard goes to the next level and offers up to 75 users and is also a domain controller.