I use Time Machine, rsync and other rsync-based tools like Carbon Copy Cloner (and previously Super Duper) to do cumulative backups.

Time Machine is generally a no brainer as it runs on a schedule and only kicks off backups when I'm wired to the LAN.

This is going to make the bottle neck of the interface largely disappear because you will only be backing up a small percentage of the data each time. I asked about a Windows solution to this issue in another thread, but I haven't yet implemented it.