I have this idea, maybe it could be a little bit useful:
Nobody is penalised. Those who pow.. "have their characters practice IG"

, still can do so like they can currently.
However, spending only small quantities of time at once for training will, on the long run, offer a better time-to-skill increase than spending a lot of time on long training sessions.
The numbers, multipliers and whatever else in the following paragraphs are purely fictional. I don't really know much about the limits and mechanics of the skill system, so they only serve to explain the idea.
You get, say, two times as much 'points' towards a new level with the skill once you only perform a limited number of such actions per RL day. Training just, say 1-20 "skill increasing actions" (whatever those may be) a day, would give the x2 skillgain for that number of actions. In order not to cause any stress the players ("omg can I chop down the tree without losing the bonus?"), there would be a small "buffer" which would not give any bonus, but where working would increase skill just as normal, before the bonus starts to diminish due to too much working (lets say, 50% of the base-action amount, so 10 "actions", maybe giving a warning.. maybe not.*). This would net you with the maximum of 50 points towards skill increase in one day without removing the bonus, at the investment of time for 20 such actions. If a person would work more than 30 actions, the bonus would quickly erode away.
30 actions = Counted as 50 "actions"
31 actions -4 points of bonus (+1 for the action) = -3 = 47
32 actions -4 points of bonus (+1 for the action) = -3 = 44
33 actions -4 points of bonus (+1 for the action) = -3 = 41
34 actions -4 points of bonus (+1 for the action) = -3 = 38
35 actions -4 points of bonus (+1 for the action) = -3 = 35
Thus the skillgain situation would quickly return to normal.
Maybe there should be an additional check for having to spend a minimum time online on that day for the 'bonus' to apply for real, in order to really reward those people who spend the time on doing other stuff ingame than skilling.
People who do hundreds of actions a day would still gain massively more skill on the short run, while on the long run this way the 'non-skillers' would have a better skills-to-time investment, IMO.
The bonus should be small enough not to encourage people to stop training and making stuff (thus not really giving a visible return at first), but large enough to make difference for those people who play a lot but find the skill system to be a pain in the ass. The balancing, multipliers and the actual number of actions allowed in the system would be left to be decided for nitters or someone who really understands the system in detail.
People are pretty clever when they seek to 'gain' something, so I'm sure someone would eventually find a way to abuse this system (too, like every other) so please don't rule it out immediately because of that.
Whaddya think?
*If the people are let to know the actual details of the system, then the a "warning" would maybe be unnecessary. However, if the staff wishes to keep the details of the system as a secret or a little unpredictable, then a warning ("You work a lot"/"You will soon lose the free skills noob!" etc

) randomly triggering anywhere between the actions 20-32 (in the example) would be nice, in order to prevent people from "counting" the number of actions to maximise the skillgain every day. We don't take that kindly around here!