First, I'm pretty sure you can use a keyboard with gmail.
As far as doing work offline, <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/... Cache</a> has you covered, assuming that by "answer," you mean "compose responses to," because if your software actually lets you respond in those situations then hot damn, I'm totally sold on it, hook us up with a link.
Been there, done that, got bored with playing that game. Why do I want something that only works half the time and shakily (seriously, look up some of the talks on the weirdness of AppCache) when I can have a nice looking, fast and reliable desktop app for whatever it was, $5 or something?
I've been using the AppCache'd Gmail app on iOS and... it's distinctly average compared to the Gmail app on Android. There's a lot web apps can do well, but for Mail I'd much rather have an actual desktop app.
And it's not just composing responses, it's tagging, archiving, deleting and so on with decent, working and reliable sync. The native app on Android rocks, and Sparrow is pretty damn awesome on the Mac.
As far as doing work offline, <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/... Cache</a> has you covered, assuming that by "answer," you mean "compose responses to," because if your software actually lets you respond in those situations then hot damn, I'm totally sold on it, hook us up with a link.