I'm working on a project where a user will sign up for an account on a touch device. (This is a one time only flow). This process involves 5 fields. From what I've read/experienced over the last couple years, it's often good to limit screens to one field, so the user can focus on that, fill it out, and continue on (via a next button or whatever).
One reason for this is that error recovery can be very tricky on these devices, and people can get confused on how to navigate fields.