Separation of concerns is the biggy.
Being able to tease these components apart makes the code easier to re-use and independently test. If you don't actually know what MVC is, be careful about trying to understand people's opinions as there is still some contention about what the "Model" is (whether it is the business objects/DataSets/DataTables or if it represents the underlying service layer).
I've seen all sorts of implementations that call themselves MVC but aren't exactly and as the comments in Jeff's article show MVC is a contentious point that I don't think developers will ever fully agree upon.
A good round up of all of the different MVC types is available here.
