Backup tool across the internet to another PC?

This tool allows you to use a friends system as a cloud backup instead of paying for cloud space.
http://www.buddybackup.com

Does anyone know of a multi-platform software that does this as my friends have Windows PCs.

Thanks Bear that looks great.

Even their paid services look excellent value for money. Makes me a little suspicious offering so much for so little cash (although excellent if they are reliable). The client list on their site is very impressive but I'm not sure how I would check whether the list is accurate (i.e not a lie). I might just email one or two of the companies and ask them.


Has anyone used crashplan ? How did you find their service?

Just backing up to the crashplan trial. All seems ok so far although it would be nice to get an upload speed faster than 4Mb/s (megabits), my connection allows for 20-25Mb/s up .