Passwords are an excellent option. I would qualify that with the following though: if you are on a
home computer desktop, I personally don't think there is a need for a
password entry every time the screen saver comes up. Especially if most of
the time that happens while you are reading over something or thinking and
actually sitting at the computer. The "password on screensaver" can be
disabled while keeping the password requirement when the user logs out.
That is the way I have it set up and use a key combo (cntrl+F11) to logout
whenever I am stepping away. This is just my opinion and preference.

Also, I'd say there's nothing wrong with changing the length of time between
screensaver appearances when it is popping up, say, every 5 minutes if that
is too frequent for a given users computing habits. It's not uncommon for
me to stare at the screen when I am writing for 20+ minutes thinking of what
to write or how to rearrange a paragraph. I'm cool hitting a button to pop
up the screen if it starts to go or goes dark. But it breaks my train of
thought if I have to actually enter a password.

Laptops, on the other hand, I keep the password on screensaver appearance
just in case the screen goes dark and I step away forgeting to log out (my
laptop turns the screen off rather than an actual saver that I see). Same
with the phone, and it is set to lock at 1 minute.

In summary, I think passwords and their implementation on Ubuntu is
generally excellent, but their use should be tailored to a user's needs
based on how a computer is being employed. I would personally be miserable,
rather than happier, if I had to enter a password every time I didn't touch
a key or the mouse for 5 minutes on my desktop. Even at 15 or 20 it is
pushing my tolerance.

This 15 minute persistence of the administrative user password when entering
sudo in the terminal, on the other hand, is one place Ubuntu should have
changed default password behaviour. Maybe by the current version, they
have. Of course, it is all pretty worthless if someone can login as root
shell in recovery mode without a password or just pull the drive if they
have physical access.