It seems to me that after reading all of the responses from the last 24 hours, not only is policing account sharing difficult, it may be completely undesirable.
What this tells me is this:
As long as achievement in this game is weighted SO heavily towards time spent, the playing field will NEVER be level.
Therefore, we're faced basically with 2 different choices:
Limit the amount of time that everyone can play, just like other F2P games with daily gating. I'm certainly not in favor of this but it would end the account sharing instantly.
Base achievement in the game on some other quantifiable value. This one is really hard. Skill would be an obvious choice IF the ability to win weren't simply an afterthought with the way the game engine is now.
There doesn't seem to be an easy solution. I can certainly understand why people aren't in favor of policing account sharing. I also understand that many people, myself included, don't have that luxury and shouldn't be penalized because we can't compete with those that do.