The E420 is exactly the same size and 5g heavier than other Oly dSLRs before it (and not significantly smaller than dSLRs from other manufacturers, e.g. Nikon D40/60, Canon 400D).
The E-410 is 5g heaver than the lightest of all DSLR's, the E-400 and E-410, but significantly lighter than any other DSLR including most other Olympus DSLR's: about 440g with battery, compared to 490g for the Olympus E-510, 522g for the Nikon D60, 556g for the 400D, and 690g for the Pentax K200D, the lightest non-FourThirds DSLR for which pancake lenses are available.
What other DSLR body and lens combination comes closest to the roughly 535g of the E-420 with 25/2.8 lens and battery?
Also, the body is distinctly less deep than almost any other, in particular being shallower at the lens mount due to the shorter "flange to focal plane" distance of the FourThirds mount specification. The shallow "lens mount to body back" distance combined with the pancake lens (none such available for EF-S or DX) reduces the total depth of the body with lens, the dimension that is probably most important to the "pocketability" of a camera.
I agree with other comments that women are likely a major E-420 target market, as is already the case with the E-410: check out the color options for the new leather cases and straps for the E-410 and E-420. But some men like me are also interested in a light, pocketable camera with interchangeable lenses.