Have both at the moment, but the X51v is sitting on the counter. PRO:The N800 has a bigger, "prettier" screen, lighter, battery life is about equal to the X51v with the exteneded battery. WM is stagnate(sp) for the X51v but Maemo is still progressing (although at a snails pace, to the general public). CON: WM has MUCH better program base. A program to do most anything you want is available. Unlike the N800 where one must depend upon the graceous programming skills of a relative few programmers. These are MY opinions for MY usage but should give you something to think about.