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I'd never heard of that command either ("lsof") until you mentioned it.
Thanks for that tip.

"$ man -k file | grep process"
I would never had thought of trying that (I'm surprised my friend didn't think of it though).
I think that actually supports my earlier statement about "intensive Terminal training".
Intensive "grep" training at a minimum.

Some one claimed that there GUI tools "for all everyday tasks".
As I mentioned earlier most of the GUI tools I've tried, aren't actually advanced far enough to replace the Terminal.

If the Gnome System Monitor was actually useful (like Process Explorer), I wouldn't have had to use the Terminal or "fuser".

As for the topic at hand.
I spend ~95% of my computer time in Windows 7.
I can complete >95% of the tasks I undertake using the GUI tools.

I spend ~5% of my computer time in Ubuntu.
I can complete ~60% of the tasks I undertake using the GUI tools.

IMO, that GUI Task % has to increase, before Ubuntu (for example) can replace Windows in the office.
You can't expect the average MS Office user to use the Terminal.