I definitely miss my G1 - I loved the slide-out keyboard, and the "trackball" pointer device. If I could have those two things in a modern phone, perhaps slightly thicker with a larger battery, that would be almost perfect.

But what perfection would actually look like to me would also being able to use a bluetooth mouse and keyboard, and (somehow) outputting the video to a real monitor. At that point, it would be a suitable on-the-go replacement for most laptop needs.