I use Dropbox for my current work/business stuff and archive stuff on hard disks. The way it hashes files to only sync up and down changed parts makes it really efficient, I don't notice it at all. By moving stuff onto hard disks, I mean not backing up at all and hoping they don't randomly fail, a massive noob thing to do. Which is a very, very bad idea. I just can't afford loads of hard drives and I keep meaning to front the cash for a RAID array or similar.
Dropbox Pro plus fibre broadband would probably work out cheaper than an NAS and drives for the first year, so it's something I've considered. The best thing about it is file versioning and a very simple interface for remote sharing (private links), mobile apps and recovery. Even with compression, file versioning with anything large can deplete an NAS in no time and you need to move over to S3 or something anyway (which Dropbox uses). The geek inside just wants my own server too much... And I have a half empty Antec P1800 8 bay silent case just sitting in my office.