Consider a Mac Mini as an alternative
I spent dozens of hours looking into Synology, QNAP, FreeNAS, and Drobo, including reading many professional reviews, user reviews, and many threads in their community forums. I walked away largely unsatisfied.
There are a tremendous number of performance, configuration, and troubleshooting issues. Also, many features don't quite do what you think they will do. For example, it is very common that iTunes support means audio only, and not videos.
I came to the conclusion that if I was looking at anything other than a basic unit, that a Mac Mini + USB 3.0 external drives was actually better in virtually every way (except neatness). For nearly the same price (or in some cases a smaller price), with the Mac Mini you get a real computer with a real operating system. You get full remote access and screen sharing, not limited, buggy web-based access. You get full drive sharing capability. You get Apple support, stability, reliability, and frequent free OS updates. You get whole-drive encryption support with no performance hits (NAS solutions often slow way down for encrypted support). You can share folder with thousands of files in them with no performance hits (NAS solutions often slow down so much when faced with this that they seem crippled).
If you want to use Time Machine, just run OS X Server on the Mac Mini ($20 upgrade in the Mac App Store IIRC) and it's AFP shared drives are valid Time Machine destinations. If you prefer more robust backup software like CCC, Mac Mini shared drives on standard OS X will work for that too.
Want to have an FTP/SFTP server? No problem! Lots of great choices to choose from. On the NAS? Slow, buggy, and never quite fully featured.
Despite the high performance of a real computer, the Mac Mini just barely sips juice when idle. It's right on par with a simple NAS unit. It runs silently. It's small.
You get a plethora of OS X server software to choose from. Heck, with a little extra memory you can also use VMWare or Parallels to run a copy of Windows and then you also have use of Windows-based server software.
With the Mac Mini you don't have weirdly-formatted drives. You can still do RAID with OS X's built-in software RAID.
There are additional benefits as well, that I haven't had to make use of. For example, I have a full, spare Mac. If my main Mac every dies, I have a backup ready! If I ever need to use target disk mode, I've got a Mac to do it with!
I also occasionally dump side work onto the Mac Mini, such as long Handbrake queues that I don't want to tie up my Mac Pro with. The Mini happily churns at it for hours on end and I have full use of my main computer. A NAS won't do that either.
Honestly, the advantages of using a Mac Mini over a similarly-priced NAS just seem completely overwhelming to me, in my opinion, and for my needs. I have no regrets whatsoever. Everything works perfectly and it is an absolute delight. And heck, I'm just running vanilla OS X, not OS X Server.
The single drawback I can think of is that with multiple external drives, it is not quite as "neat" of a physical package as a NAS unit is.