Question : Problem: How does an i7 2.33 GHz processor REALLY stack up against, say, an AMD X4 2.8 or 3.0 GHz processor?

I'm considering future upgrades, and understand not so much about hardware; just want to be prepared so I have an optimum system as I move forward.

Answer : Problem: How does an i7 2.33 GHz processor REALLY stack up against, say, an AMD X4 2.8 or 3.0 GHz processor?

Typical results from the tasks you list (minus the office productivity) are highly impacted by multi-core in the "more is better" fashion.  

This link is a bit old, but it gives an example of how more cores makes for faster video encoding:

http://public.sheet.zoho.com/public/daatyahoo/lxuW1aq6t%2Fa19PMsgc%2BiA5ou3X0xEWUP

you will notice that its not linear having more cores, and the i7 is seen as an octal-core.

MSOffice software unfortunately doesn't really take  advantage of multi core though, so you will see only a minor performance increase using an i7.  Same with web (unless you use a multi-threaded browser like chrome)

Anything with recording, encoding, editing, etc with video though loves more cores.