There's a lot of positives to using a Mtn. Bike as a cummuter. They're nimble, responsive, quick, durable and fun just to mention a few. I'm just a few weeks into trying my Volae SWB Recumbent as a Day-Shift commuter. I'm not overly convinced yet that I like it for that purpose all that much yet, but then I've only got about 125 miles on it this season. It's been a strange Spring and rain puts me on the Mtn. Bike as I don't relish sitting on a wet 3" thick foam sponge (seat). One thing I do know is that it feels great to whiz down the road on my old Trek 820 while commuting on the night shifts.
I'm keeping an open mind, well I'm trying to anyway. I'll alternate between both bikes all season just to ensure they get an even shake, but I suspect I'll be using the Mtn. Bike exclusively for commuting next year.
I can't offer any info on forks as I don't know much about equipment qualities and/or comparisons.