I used to ride my mtb on the road all the time as it used to be the only bike I had. I still ride an mtb on the road in the winter to commute as it is better at withstanding the potholes of doom in the dark than the roadbike (it also has disk brakes which are much more confidence inspiring than the roadie brakes).

In order to make it a more pleasureable road experience I have done the following:

1) Slick tyres, pumped to max pressure - I now have a dedicated old commuter but originally I swapped between two sets of tyres, one knobbly 2.1s one slick 1.5s, that used the same size innertube (skinny slicks need skinny tubes) it could be a pain but I turned into a demon tyre changer - which after Tuesday nights performance I'm definitely not anymore . It made the MTB fly along and I generally only ride a bit slower than the roadie but for more noticeably more effort.

2) Rigid forks, light but sturdy enough to handle potholes but no bob. Some sus forks can be locked out or air forks can be pumped hard (just remember to reset them before going off road). The bob is only really noticeable for standing pedalling anyway.

3) Bar ends - Give a choice of hand positions, still not as good as a drop bar as you can't reach the brakes etc but still better than a single hand position all the time.

The roadie is still the best tool for the road but on winter commutes the MTB feels indestructible (and I've tried) which is what matters to me then.