Mac OS X - hands down Time Machine [USING]. It is the most convenient game in town, being distributed with the OS. It has overhead that is not really noticeable in time or space, is easy to use for determining what and what not to backup. It is also the only backup system where I have actually had to use. A motherboard failure which killed the graphics display forced me to bring my laptop in for repairs while I was preparing to complete my Phd thesis. I was not going to wait a full week for it to be returned to me, so I promptly bought a new MacBook Pro and tried restoring my old machine state. With some minor problems, it worked like a charm! I was extremely impressed. Not only was my data restored, most of the appropriate parts of the operating system settings came back online smoothly as well.
Linux:Ubuntu - It looks like Ubuntu 11+ packages a simple backup utility called Deju Dup [INVESTIGATING]. It looks simple and meant for backing up user data (which is fine for Linux nowadays since it is relatively simple to re-install into a fairly usable state from the start). I can see it being valuable for backing up smaller documents and data files, but not necessarily huge experimental data.
Windows - I have paid for and tried Genie 9 [REJECTED] for a while. It looked very promising at first and came with accolades from various large organizations using it. Unfortunately, the downsides became clear the more I used it on my PC. It suffered from extreme overhead in both space and time. It was set up as a "service" and would kick in the moment the PC was booted up. That might work well for company servers that stay up all the time, but the overhead due to a startup was just overwhelming ... the PC had been observed to stay unresponsive for something like 5 minutes! There was also no convenient way to tell it not to monitor changes to Firefox's cache directory (It is supposed to avoid IE's). As a result, it was constantly trying to back up the changes there and I ended up with only 23% of space left on a 1.82 TB drive after almost a year.
Windows - I am looking at Cobian Backup 11, Gravity. It is free and looks promising for my purposes.