Hi Adrian,
Developing on a mobile is really no different than dealing with a web browser - the only difference is that *you* need to behave like the browser, instead of the browser handling all the details for you.
Think about what a browser is actually doing when you click on links, log in, and so on. You click on a link, which causes the browser to make a HTTP request; the server gives you back a HTTP response, which it renders.
A mobile platform is no different, except that *you* need to do the "request" bit. So - you write code to issue a HTTP request (in response to a touch event, or whatever); you get back a response, and "display" it in some way.
Of course, a browser also handles things like cookies, so once you've logged in, you stay logged in; if you want to do the same thing on a mobile platform, you'll have to work out how your platform of choice (and the API you're using on your platform of choice) lets you manage such things.
It doesn't matter whether you're logging in, registering, or displaying a list of stuff - it's all just HTTP, appropriately by the "client". The fact that the client is a browser or an Android phone doesn't matter.
Yours,
Russ Magee %-)