I use a number of File Syncing systems, each for different jobs and they all work great for me.
1.) FreeFileSync - I use this to do a mirror copy of my <Username> folder onto an external hard disk drive. I run this every once in a while when everything is working fine. The first run takes ages as there is so much to copy but every other time it only copies new or updated files.
2.) Windows Live Sync - I use this to sync a number of different folders over to my netbook from my desktop pc. It must be online to do the syncing but it does not keep a copy online so you cannot access your files anywhere whcih is not an issue for me. It works flawlessly and each time I ahve both my desktop and netbook switched on then the files sync pretty much instantly and without me knowing!
3.) Drop box - I use this more sparingly and just pop a few files into my dropbox so I can access them elsewhere on another pc or send files to friends. I see Windows Live Sync and Dropbox different as drop box just deals with one particular folder. Windows Live Sync allows you to syncronise multiple folders anywhere on any pc.
Hope this helped
Regards,
Neil