hopefully someone with some experience in real-time mirroring programs will post a more knowledgable reply,
but you've pointed out a kind of program that maybe i should have addressed in the backup guide, and maybe i should ammend the backup guide to mention.
personally i don't use a mirroring app like this only because i am reluctant to have programs running in the background that i think could consume meaningul amounts of the cpu.
but on the other hand such a tool seems like it could be undeniably useful especially for people who put a premium on not letting any amount of time go by without having important working files backed up, and who are not as concerned with the minor hit in performance.
what's nice about these programs is that as you say, you just set it and forget it.. maybe someone here can explore this topic and it might make for a good follow up guide to backups; there is always more to say about backups and maybe a part2 would be a good idea in a month.
i like the screenshots of mirrorfolder which shows it supporting some archiving function - that seems like it would be very useful..