CrashPlan has this cool feature where it watches for new and changed files (and directories) in real-time; it immediately notices when there's something new, and schedules it for the next backup.
On Linux, this is done with inotify. This usually requires a little bit of fiddling with sysctl(8), since the default maximum number of watches allowed per user is typically much lower than the number of entries in the backup file selection.
However, you may find that this feature still cannot be enabled, no matter how high you raise that maximum number. Turns out that CrashPlan first checks the kernel version for inotify support (which was introduced in 2.6.13), and cannot parse a version number with only two components.
Guys, seriously? Seriously? It's been more than three years since 3.0 was released. This should have been fixed a long time ago, and I most certainly shouldn't have to write a goddamn uname library wrapper to make it work.
That being said -- once you've finally got it working, it's really cool, and well worth the effort.