I have been using Arq as my primary backup solution (on the desktop/laptops+ side) for 1 year now and have replaced crashplan, dropbox as well jungledisk with it during that time so I hope some of the ideas below on ways to sync files in a safe matter will help (but not work for everyone). That said I would recommend to use Dropbox, Google drive or whatever the right tool is for you to store non-sensitive data as those products are designed for multi user _easy_ file access and sharing (mobile client etc) and then still rely on Arq for the actual data backup / integrity process.
* As mentioned - just use Dropbox/google drive etc and have Arq back it up. If you work with OSX native file formats Arq will do a great job to make you feel save in case anything goes wrong during a sync (conflicts, open files etc). I would not relay on the 'backup' feature of each individual product due personal experience.
* Use Arq by itself by comparing the "Last Modified" column of the file / directory you are about to use with what OSX Finder shows and if out-dated replace the whole file/directory. This has the obvious data size / bandwidth limitation but can work better and faster then most existing products as _you_ can pick which file you want to grab (think if you have large amount of storage at work and only want to grab one file at home). This workflow also ensures that whatever you store and transfer that way is client side encrypted / secured the same way as all your backups.
* Use OSX's "Disk Utility" to create a (spares) Disk Image and have Arq back it up. You will be able to password protect, mount it as a regular disk (have a common mount point between all machines) by using the same "compare 'Last Modified' before starting to work on it' workflow. This works great for sensitive data and even if you happen to leave the image mounted on multiple locations an additional backup of the disk's content will allow you to just grab whatever you were working on last vs. syncing the whole image.
* Use an OSX native archive tool and synchronize that "archive" file using the same "Last Modified" workflow with Arq. Arq will show you when the "archive" was last modified vs. individual files. Examples (Devonthink, EagleFiler, Yojimbo)
The "locking" issue Stefan mentioned was the biggest source of problems I run into with other tools (think if your laptop crashes while working on something, you keep something open after leaving work, "certain" issues with OSX native file formats etc) so one year later I am exclusively using Arq (and http://git-scm.com ..) to handle all my personal data.