Advice wanted - external drives and backup strategy

The backup solution for my Mac (2005-era dual-core G5 Powermac, running OSX 10.4.11) is currently as follows:

- important current work done via Dropbox
- Daily backup of key settings to my iDisk via OS X Backup
- Various daily/weekly/monthly backup jobs of documents, pictures and music from the main 250Gb drive to a second internal 250Gb drive I installed a couple of years ago.

Clearly this doesn't give me off-site backup and frankly I've accumulated enough stuff that the second drive isn't really big enough any more.

Now, given that I rarely go more than a month without visiting my mum down in Woking it occurs to me that I could get two 1TB external drives and make a habit of the following:

- Do a full backup onto Drive 1
- Do daily incremental backups onto Drive 1
- When I visit my mum, take Drive 1 down, leave it with her, and pick up Drive 2, left on my last visit
- Do a full backup onto Drive 2
- Do daily incremental backups onto Drive 2
- When I visit my mum, take Drive 2 down, leave it with her, and pick up Drive 1
- and repeat ad infinitum

This way I have a local backup that is at most a day old (and as I said, most stuff I am actively working on I host via Dropbox so is continuously backed up off site) and have a full backup no more than a month old some 40 miles away.

Any major flaws with this plan? And any particular reccomendations for 1TB or similar external drives that will work well with my setup?

Heston Blumenthal's *special* sauce

Via Stephen Fry on Twitter, possibly the most unfortunate truncated URL ever.

Carrots glazed with cumin and orange, or, to give the direct link...

http://www.bbc.co.uk/food/recipes/carrotsglazedwithcum_80467