I'm listening to the latest Mac Power User podcast. Generally, while much of it feels like an ad, there's definitely good stuff in there.
Anyway, they spent a lot of time talking about the incremental nature of a backup strategy.
First, I'd argue that any non-incremental backup utility is fundamentally broken. Second, rsync is included with OS X.
rsync -vurpt source target
In an initial execution, it's equivalent to copying everything over. But it saves timestamps, so on later executions, it'll merely incrementally copy changes.
Of course, time machine also does things right (actually, it does some really funky things behind the scenes that does even better), as it saves multiple versions, whereas rsync just has one version of the tree.
One advantage of rsync, though, is that you can just back up part of the tree. And another is that you can add '-e ssh' to the command to copy things remotely.
And I'm surprised there was no mention of backblaze, to keep off-site backup copies. It sounds really good, and I've been thinking about it. I haven't, mostly for security reasons (I'm super paranoid about these sorts of things), but it seems really good.