[KaVir]

I don't think it's "unfair", I think it just doesn't suit your personal playing habits. But whatever system is used, it's not going to suit everyone. Even if you were to give every player a fixed amount of exp, whether they're online or not, you'd have hardcore players complaining that they should be advancing faster than those who play less.

The standard approach for most muds is that you earn exp for killing mobs. But killing takes time, therefore you are indirectly earning exp based on hours played...and you'll hear plenty of players complain about how much they hate grinding.

By simply awarding exp based on online time you get the same end result (exp for playing), but the players don't have to grind. They can kill mobs if they wish (perhaps for collecting treasure), or they can do some crafting, or exploring, or roleplaying, or just socialise if they prefer. You're basically shifting the emphasis from "kill lots of monsters" to "play the game the way you want to play".

My current mud doesn't give idle exp, but it does award "boost points" the first time you log on each day, and these can be spent to speed up your advancement. If you're out of town with no internet access then you would still miss out, but if you're just very busy you could log on then immediately log off again. You could do this for up to 4 days in a row before reaching the maximum number of boost points, so this would certainly cover the "4-5 days per week" playing style you mentioned earlier.