Graham
I've had no problems with mine but I have heard a few worrying tales.
Finish to the lower fork legs and brace is a bit suspect but I think the GS may suffer the same fate. The odd gearbox and shaft drive requiring major surgery but again I seem to have read the same about the GS.
With regard to the Replika in particular there has been talk of the sponsors stickers peeling off when washing / polishing as they're not lacquered over - get this done before you leave the showroom to avoid losing the bike for warranty work
Apart from that it all seems fairly sound. This is my first boxer having only had jap fours and K series BM's up until now so it's still new ground for me.
It was a toss up between the GS and the S but being a bit of a speed freak I went for the S with it's few extra horses and top speed which to be honest probably doesn't even become apparent in the real world, but hey.. I'm happy
I understand the S has a better riding position and weather protection than the GS as well but this is horses for courses.
The only disappointment I had was the lack of underseat storage... there isn't any! Bit of a shock after the K's.
If you want some more info just ask. There are also some more acquainted with the S and it's foibles at this forum:
http://autos.groups.yahoo.com/group/boxertrix/
Not as easy to navigate or search as this one but throw a stack of questions in and they'll be answered fairly quickly.
Cheers
Adam