Back up issues

This depends largely on what your backup schedule /requirements are. For example a reliable back up solution for me may mean an up to date backup every hour(+multiple copies sent halfway across the world to another computer, or something like that), whilst for you it may mean to have your documents /photos copied over to your external drive (or vice versa).

I know these 2 examples are at the opposite end of the spectrum but the difficulty in setting up each one is also very different.
Could you elaborate on what you want to achieve please (just documents you want backing up or your entire installation, do you want to backup your operating systems seperately (so you can restore them one by one) etc etc)?

Here is a quick summary:

WIndows 8:

pros--
if the system image tool is still present you can back up your entire installation. A good app for windows back up is todobackup, amongst many others , some are free others are about 30+£ but seem to work well. On a basic level copying your documents (manually ) as a simple as copying your user folder (or your home folder in ubuntu)

cons- you can only backup your windows installation and not ubuntu .

Ubuntu

Plenty of backup solutions, some require command line usage (rsync for example, although you can get a graphical user interface for it- grsync).

Some good ones :

rsync- command line driven but very good, here is a short tutorial ( http://www.jveweb.net/en/archives/2011/02/using-rsync-and-cron-to-automate-incremental-backups.html )

or any of these

http://www.thegeekstuff.com/2012/05/backup-ubuntu-desktop/

Please indicate whether you want to backup just your files or your entire harddrive, (so that in event of failure you just put the backup on a new harddrive as if nothing happened).