As it happens I just spent about two weeks photographing landscapes almost exclusively with the 100mm D-FA WR on a Pentax K-3, thus most of them were focused at infinity or long distances. At a first glance (I didn't get to process the raw images), I can say that the 100mm perspective gives the landscapes a unique perspective. (Perhaps it's just the novelty factor for me at this moment, but I enjoyed it more than with "shorter" focal lengths.)
Now about your question regarding sharpness: after a quick look I am not that sure that the images are as sharp as I would have expected for this lens (given how sharp it is at closer focus distances), but this might be perhaps due to the haze, hand shake (I didn't use a tripod), the shake-reduction system, mis-focus, or any other issue not pertaining to the lens. (As said the lens is sharp at close focus distances.)
However there is one serious drawback for the 100mm D-FA WR when it comes to landscapes: auto-focus is quite unreliable at infinity (even in bright day light, with the center-point and in single-focus mode), and I always had to resume to live-view and focus-peaking to manually adjust the focus. The problem wasn't the focus hunting (it happened only twice), the camera did catch focus quite instantly, but the focus wasn't quite "perfect". Thus my conclusion regarding focus was: always manual focus with live-view and focus-peaking. (Auto-focus in live-view is equally unreliable.)
As a side-note regarding focus, just as someone else said, it is so easy to de-focus the lens by even the slightest touch, and sometimes I had the impression that even pointing the camera downwards (to look at the LCD), would de-focus the lens (perhaps a form of "focus-creep"). Thus before any image taking: switch to live-view, enable focus-peaking, tweak manually the focus, exit live-view, compose, take image.
Regarding chromatic aberrations, it does indeed has purple-fringing, visible even in the viewfinder, but this does seem to disappear by F/5.6, thus I wouldn't say this is a problem.
Summarizing: nice perspective for landscapes, sharp enough especially for web-shared images, but almost exclusively manual-focus (with live-view focus-peaking) at infinity. Searching for an non-macro alternative.