I never have managed to get a game of Ars Magica up and running, despite at least two concerted attempts. We even got as far as full character sheets. Why didn't it happen? Perhaps the degree of world-building needed looked too daunting -- though you wouldn't expect that to deter a group battle-hardened by Tekumel and Glorantha.
Mike and Roger were talking about it this month on their Improvised Radio Theatre With Dice podcast. I'll put money on their campaign happening before mine. (I'd even consider putting money on their campaign actually happening.) And I was reminded of one aspect of the Ars Magica rules that was certainly original but that never thrilled me. The troupe system.
I prefer to really steep myself in a character, which means one character at a time. In Ars Magica you play the magi and also their companions (non-wizardly adventuring friends) and sometimes the magi's servants ("grogs") -- the point being that the magi initiate things and formulate plans, but they don't all swan off adventuring together on a regular basis. For me, one of the line-up would feel like my real character and the other two would just be NPCs that I'd play for the sake of the campaign.
The reason for the troupe is that you typically have your group of players turning up each time, and nobody wants to sit out in the kitchen, so the magus/companion/grog arrangement ensures there's always a character for everybody to play. But hang on a tick. If you're playing online, you're no longer constrained by the need to physically assemble a limited number of players at the same time each week. Now you could have some players take the magi; they might be the ones who can't turn up regularly or who are living a long way off and couldn't travel to a physical session anyway. A different group of players could then take the companions. You can assemble a regular game around whoever can show up (usually the companions and one or two of the magi) and keep the grand planning between the magi for special sessions.
By-the-bye, I like the idea of some characters playing strategically while others get their hands dirty. You could use it for an SOE game -- any war-based campaign come to that. Or it could be a Star Trek style exploration game, with the regular weekly players comprising the away team and those who only have odd moments through the week playing the bridge crew.
Also it occurs to me Ars Magica would be a great system for a Wizards of Grand Motholam campaign. Now will I buckle down and run it? I guess we'll see.