<< I installed 7.2 on my machine a few weeks ago. How difficult will it be to upgrade to 7.3? What is involved? >>
I've upgraded Red Hat Linux a few times. I've upgraded SuSE Linux a few times. In those cases, the upgrades worked well.
I would recommend the upgrade only with a "minor" version number change. I.e. from 7.2 to 7.3, but not from 7.3 to 8.0.
In my experience, upgrading Linux is much more reliable than upgrading Windows. MS is constantly reinventing the wheel, and with installed 3rd party software, upgrading Windows is often an iffy proposition.