I'm digging up this thread as I just got
a KSM141 and thought I'd share my impressions.
Essentially I agree with xstatic. The 141 has a nice top end. I always fancied myself a lover of flat-response microphones, so it hurts me to admit the 141 sounds better. I mainly use SDCs for string instruments, and on the following instruments, all from two feet away:
harp (29 string folk)
classical guitar
dulcimer
violin
I only preferred the 81 on harp, where it brought that rather quiet instrument forward, where the 141 left it distant and too crinkly. On classical guitar the 141 added a nice top. The 81 made the dulcimer sound like a little wooden box, which after all is what it sounds like, but the 141 lifted it to a higher plane.
I experimented quite a lot with violin. Using a placement towards the side of the violin, chest high, the 141 shone, retaining enough high end while still being balanced. The 81 suffered, yielding a fiddle tone but with odd resonances. I don't have an expensive violin, so maybe that is what it sounds like, but like the dulcimer, the 141 made it sound better than it does.
There are two other characteristics of the 141: it's much hotter than the 81, which I find helpful. At the same time it is less noisy, although the 81 is plenty quiet for my uses.
Second, in comparison, I didn't note the reknown "in your face" character in the 141. The 81 definitely has it, which helped on the harp, but the 141 always gave a better sense of space.
One minus is that you need some sort of tool to move the pad and rolloff switches. That's a pain, but I never use them, since I have those features on my pres.
I didn't make much use of the omni setting: the tone seemed about the same, but the rear sensitivity picked up a bit more room noise, as I didn't have my studio on full quiet mode. I will find it more useful for location recording.
In conclusion I'd say the 141 is a good step forward for not very much more money.