The SEAS (School of Engineering and Applied Science at Harvard) is a actually surprisingly decent. The one thing that gets some people is that CS is taught from a very mathematical bend - about a third of the CS classes don't require any significant work on a computer (besides typesetting the problem sets in TeX). I actually prefer it that way - I'd rather focus on theory in class, I can pick up the idiosyncrasies of the tools and languages on my own time.
I understand that Harvard's Math department is pretty impressive too (near the same level as MIT/Princeton/etc).
Depending on who I'm talking to, I've heard that Princeton, MIT, and Harvard are each the best in the world (for undergrads). I'm not really in a position to judge, so let it suffice to say that all three are fairly impressive.
Princeton is first and Harvard, MIT, Stanford and Berkeley are tied for second. Harvard is always mentioned as one of the top Math depts. more so than MIT in my experience.
I understand that Harvard's Math department is pretty impressive too (near the same level as MIT/Princeton/etc).