I did. In fact, I used viper mode (vimpulse) for about three weeks before deciding it was worth a shot to just try vim proper. I haven't really looked back. Viper was alright, but there were far too many moving parts in that setup.
I could never leave Emacs at this point, though. Elisp is just too great.
When I originally moved from Vim to Emacs, I found Viper /harder/ than just learning regular ol' Emacs. I assume "Moving parts" refers to exactly the same problems that I had. I could explain more, but it would take time, because I need to figure out some examples instead of explaining my vague impressions of a few years ago.
Point is, as an avid emacs user, I totally get where he is coming from.