...and StatCounter also reports that Windows XP - the most frequently pirated OS in existence - is still powering along at 81% Coincidence? Nay, I think not: http://www.troyhunt.com/2010/08/aye-pirates-be-reason-ie6-just-wont-die.html
I don't believe it will partially backup the changed component of a file if that's where you're coming from.
Worst thing about piracy in China? I reckon it's a significant factor behind *@#%#$ IE6 just not dying: http://troy.hn/cOySCO
There are plenty of easy ways to find the additional local capacity, but in terms of backups, IMHO any practice that requires you to manually perform tasks is setting you up for failure. You'll forget to put that backup disk at your mother in laws or you'll carry a few weeks of extra risk because you've been busy or any number of other reasons. And as for keeping backups at home, there's the risk of burglary, fire, flood, four horses of the apocalypse etc, etc.
There are some great online backup services these days that take care of the whole thing for you. Point it at your data, define a backup schedule and let it run. SugarSync gets some good feedback. Personally, I've found Mozy very good and for the sake of $5 per month for unlimited storage, I reckon it's a bargain. Here's my setup: http://troy.hn/bhP4F9
In terms of network and speed, even from Australia (typically slower connection to US based services), I pushed up over 100GB in about 4 days recently. A combination of fast, cheap bandwidth, unlimited storage and a reasonable rate of data collection makes this perfect for the scenario you describe.
Help me, I'm a prisoner in a Fortune cookie file!