Big space... for your e-mail at least. Gmail is now allowing attachment of up to 20MB. Prior to this, the limit was still a generous 10MB...but sometimes we've found ourselves maxing this out lately.
With sites like Flickr and YouTube allowing us to share media without having to worry about file size, we'd guess Google is just trying to stay current. With Gmail now allowing larger files, we have one less headache when sharing our media.