I certainly have considered them, but I'm already paying for dropbox and flickr and a vps and domains. I try to keep recurring costs relatively low.
I use dropbox to back up important files and flickr is a backup for my photos. I'll be getting a NAS to provide at least some local fault tolerance for storing things like photos, music, and movies.
One of the reasons I went for a Synology is that you can run the CrashPlan client on the Synology itself. It's unsupported, but easy to do and has worked well for me.
If I were dealing with that level of photography here's how I would consider setting it up:
I'd buy a home NAS and shove it full of disks (a Proliant Microserver can take 4x3TB drives easily, 6 if you want to get creative with ports and USB bootable sticks) and run it as a RAID-5 array. This cost me about $600-$700 a couple of years ago, drives inclusive. My array sits on a bookshelf, tucked away, almost silent (drives are the majority of the noise sometimes) and low-power. RAID gives it pretty decent durability so if you do get a hard drive freakout you're able to correct pretty easy. When one of my hard drives went dicky, I just ddrescue'd it across to a fresh drive then let the RAID array rebuild the bad data (RAID-Z is so sexy but that's another topic). You could probably just DD the thing and rely on the RAID checksums to do it or even just checksum the entire lot, depending on the volume of data.
Then I'd link Crashplan or Glacier to those folders and have it periodically diff/sync the data (e.g: overnight once a week/month). I don't have any such setup myself but I have read posts on forums from guys who have set this up as automated syncing of folders and they seem pretty happy with it. This is essentially an insurance against fat-fingeredness or your house burning down.
Now you have an offsite backup that is always relatively recent and an onsite backup that is free to access to your heart's content for modification through almost any medium. Yearly crashplan unlimited access costs $70 for a single device which is really all you're after, because your working storage is your NAS and the NAS is all that'll ever be touching the crashplan storage. I don't know Glacier pricing but I'd imagine that for some workflows it could be beneficial and for others it could be detrimental.
Dropbox can be set to sync with a subfolder so that if you take images on your iDevice or equivalent it automatically syncs them via dropbox to your NAS. Dropbox can also act as your working directory for any images you may be tinkering with on a remote device that can't just access the NAS outright. Rsync can be used to transfer files out of the dropbox folder to the main folder or to a 'to be sorted/postprocessed' folder on a periodic basis - essentially, every day you take a bunch of photos, that night it checks dropbox for those photos and shifts them out to free up more space. The NAS is a full linux install so it's flexible on what you can do.
The only downside I can see here is that you don't have every single image in the cloud, available to every single device at any given moment. I'm not sure if for your gigabytes of photographic memories that that's necessarily an issue, nor am I sure that if you're primarily editing stuff on a fullsized computer with e.g. Lightroom that is usually on the same network as the NAS, that it's a problem either. Sharing of data can be facilitated through a public dropbox folder that you just copy stuff in to when you want to share those images.
Anyway, from the perspective of someone who doesn't actually do this. I'm sure there's tools I don't know about that could slot in to this workflow and solve other problems that may affect some people. The beauty of it is given that the storage is yours, local to you and based on a full linux distro, you're free to do just about anything to it. Change backup providers? No problem, just resync all data. Workflow changes and you need a new feature? Find it and install it.
I look forward to hearing feedback on why this may/may not work for you :)
