what I use the 100 for, and what anyone should use it for, is getting shots on the street that would otherwise be difficult.
That's a bit perscriptive for those of us who aren't into street shooting! (and I don't do portraits either...)
Seriously, I used the 100mm on about a quarter of the landscapes I shot on the Bronica on my recent trip to Svalbard (and I've finally got access to a scanner that will take 645 slides so I can post some of them soon!) As has been said in other posts elsewhere, you don't always want a wideangle for landscapes, and you can't always 'step forwards', particularly if you are on a boat or a cliff...
I'm sure there are collectors and completists out there driving the price up which is a shame - I paid £350 (mint - boxed) for mine last year, and its definitely worth that in the context of the rest of the camera system. Out of interest, does anyone know how much they were new, before they were discontinued?