There are some projects for Linux that do file system mirroring over a network connection. But they are mostly experimental.
Everything I do involves a scheduled sync. Cron in Linux, and the Scheduler in Windows.
I haven't looked at SyncToy in years. But if it is only synching the changes, it might not hurt to run it every hour. It depends on how badly it degrades performance while it is running. The other thing to watch out for, is reading in a large amount of filesystem data can also purge all the good disk cache, and slow down programs until they've reloaded themselves. If that happens every hour, then you could end up never building up a good cache set for very long.
Daily backups are usually good enough for home use. But experiment, if you want to try more often, see how it affects performance.
Look for Time Machine on the Macs (it's part of the later OS X releases), see if it will backup to the network drive (I know it does to Apple branded devices).
