MO,

I would say yes as witnessed by father, uncle and brother using it and the only support questions I have to answer is when they sometimes forget their passwords!

My uncle slips in a silver disk from the Sunday papers and if it is a DVD then VLC does the business otherwise Soundjucer offers him a play list for his perusal. With Firefox and addins like noscript, adblock+ after a bit of white listing things are safe and sound as is Thunderbird and Gmail. As the users run on  a non-admin account this also helps and once every couple of weeks I pop over for a chat and run updates on an admin account they can not access. The Gnome desktop may lack the start button and Windows logos but I reckon the menu system can be grasped after a few moments instructions. I can not see a downside to this system for you father  may be picked upon by his mates down at the pub out of pure jealousy because his machine just works and is not virus ridden and sluggish most of the time.

Ps I expect that the system comes pre-installed and all you have to do is pick and assign user names and passwords for new users