You don't 'sit and wait' with either of those services, DropBox transfers in the background, and mozy is a 'backup service' that waits until your computer is idle (normally, you can force a backup obviously) at night before performing its transfer to their servers.
In both cases the data resides primarily on your hard disk, it's just backed up to the remote location when possible. Both also give you versioning support, meaning if I make a mistake and accidently delete something within 3ds max on my 3d model, I can look at it a week later, and think 'hmm, that's not right', go to dropbox or mozy, and select to recover the version from a week ago - in both cases such versions don't seem to count against your storage limits either.
I'm by no means suggesting that people keep their entire library of downloaded cdp's on such services, but if you create content, you should very certainly be keeping your 3d meshes and textures on a backup, and local backups are NOT a complete solution. Too many times I see 'well, he/she lost the mesh' used to describe why reskins can't be improved. And even many creators that have left trainz after losing all their work and feeling utterly gutted that their hard work is gone.
Both of the services I mentioned, and pretty much all of their competitors, are secure and trustable, in the case of Mozy you can provide the encryption key that the program uses to encrypt the data - so even they can't access the contents of the files.
I'm well aware of backups and data security, and the fact that Mozy and others are most likely using a changed-data backup sytem. In other words, your data is only backed up when it has changed from the last backup. This works well until you do a restore of everything from scratch. The archive bit is reset, and therefore according to the backup client, nothing has changed since the previous backup.
The fact that the software would be running its thing in the background would drag down the performance. My machine is never really idle, and when it is it's off. I've run services such as this before, and found the tasks running in the background to be a drag on performance.
For decades I was involved in datacenter backups, and relied on various media that was available at the time. This ranged from tape to worm drives. All of this media at the time proved very reliable, and by keeping the data off-site the company would retrieve it only when there was a need for a restore. This works well in a corporate environment. These off-machine storage systems have proven their worth in their time, but as data size has grown, the backup time window has shrunk.
As hard drives have grown more reliable with much lower costs, they can be used instead of tape, which can become unreliable with age; it's the nature of the beast. In fact Mozy and others most likely use SANS or iSCSI networks configured with drive arrays setup to emulate tape drives. This is the solution to tape, which wears out and limits the amount of space. Storage cartridges now are hard drives, and no longer DLT tapes.
Like many people here I have, as I said above, multiple hard drives. One of them is something I've mentioned before, and highly recommended. Thermaltake's BlackX, which sells for about $60.00 US, is a USB based unit that holds any SATA drive. Simply plug the unenclosed hard drive into the base and go. It's hot swap-capable, and works well.
http://www.thermaltakeusa.com/Products.aspx?C=1346
I've setup a simple routine, which is not unlike what your software is doing for you. I backup my data, which is mostly my route and documents to my internal backup drive. At the end of a week, I then offload this data to my externally mounted 1TB SATA drive. I catalog my data by date, and can simply find what I am looking for.
I suppose it's all about priorities, but personal data to me doesn't have the priority-level that corporate data does, which losing that can cause legal and financial inplications in a big way. The fact that you are a content creator, perhaps puts you in the former category, but again having yet again something else running on the machine along with the antivirus/firewall, and anything else that everyone puts on there, only adds to the performance drag on the hardware.
John
