We also have a Synology. I host a DS1512+ at my place and have 50/25 internet. There are smartphone apps, you can run your own dropbox-like cloud sync, host your own photos... pretty much everything OP wants to do. I have 3 WD Red 3TB drives in RAID5. (Already had one disk die, overnighted a new one, the array rebuilt with no problem and I had full usability of the system the entire time. The replacement drive is now a hot spare.)

We use plex very heavily on it, and it works well. All our HTPC boxes are plugging into my house wide gigabit, but streaming over mobile internet works extremely well with plex. In some cases I spin up a VM on my desktop with plex server on it and use that to stream from if I need extra transcoding power. Since I have a DSLR, I end up taking tons of photos. I have an Eyefi card which I've configured to upload directly to an "instant uploads" folder I've configured in PhotoStation. I come home, and my camera automatically begins uploading the photos to my NAS as soon as it sees my wifi (when I enabled the transfer), and I can view it on my phone or laptop as it uploads.

I own a Synology NAS. It's great and includes plenty of useful features, including a dropbox/box-like application where one can sync files easily to any of their devices. No storage limit (other than the NAS and the storage of whatever devices I'm syncing to) and there's far more other things you can do besides the dropbox-like feature. Why should I pay a monthly fee to let someone else have all my important files, when I can easily host my own? It works great and I never have to worry about some provider getting hacked or changing their TOS.

Of course, one should back up their NAS (and there's plenty of easy ways to do so on the Synology), but the point is if people are concerned about their data, they should take responsibility for it.

Rob,
I've been reading this site nearly since the beginning (though I'm mainly the lurker type) and it has always provided me with some good reading material. I'm happy for the success you've had in this venture and in life and I'm sure that after you take a nice break that you'll find some other thing to be hugely successful in. The comments on your last post are a testament to how many people will miss you on this "little" website you've created.

Thanks and good luck!
James