Again not to diminish puelocesar's work.

But this is, in all actuality - a glorified web browser (highly optimized for Maemo) the pretty interface in gmail is using the iphone browser user-agent (this can be faked in other browsers as well).

Furthermore, try http://mail.google.com/mail/x/gdlakb-/gp/

Like I said you can go to other sites using it. As far as what the "app" entails, puelocesar added kinetic scrolling, zoom and stuff like that.

If you want GV, yahoo mail or other sites to look pretty you need an optimized CSS. As GV and yahoo mail don't have nice mobile versions, a CSS style would need to be hand-coded. I started trying but it's a major pain to make it look nice. Look into userstyles.org if you'd like to contribute.