I dont have experience with entourage, but I do use Gmail and I adore it.
I have over 200 saved emails and I am only using about 16% of my alloted space.
I can access my email from anywhere when I have internet service.
I dont have to remember a pop server number or program anything. It has all sorts of good ways to save stuff and lots of easy to use settings.
Im not the biggest computer dork anymore, so I need something quick and easy and I love gmail for being it.