Another assumption that seems to be going around is that a wizard who is compelled to accidentally hex something is doing so intentionally, and that the character or player is therefore actively trying to screw over another player.

To be honest, if I had a player who wanted to hex something another player was using, I wouldn't allow it as a compel. It's a poor example, really, because a GM who makes that compel is causing problems for a particular character that shouldn't happen, narratively. Looking back at my last post, I don't agree with what I said anymore.

For me, the purpose of compelling an Aspect is to bring problems to a character that suit that character's narrative and personal plot. So unless a mortal has an Aspect that reflects his association with wizards (Like's Billy's "Harry Dresden Is My Friend" Trouble) then I wouldn't use a compel to cause problems specifically to them due to a wizard's presence.

So, say Harry and Billy are driving along in Billy's SUV, using a GPS to find a quick route while on a case. I might compel Billy's "Harry Dresden Is My Friend" Aspect to cause the GPS to get fried, since that Aspect reflects the difficulties Billy experiences due to hanging around with Harry.

The important thing here is that, if Harry was driving with, say, Kincaid, who also had a GPS, it's a different situation. None of Kincaid's Aspects are related to Harry or any wizard, so Kincaid's stories don't feature problems and delays due to Harry's presence, because those aren't thematically appropriate for Kincaid. The importance here is more on what narrative elements are specific to the characters involved, not what should "realistically" be a consistent effect.

I agree with this. Basically if you compelling an aspect then it should in some way be creating a complication for the person who has the aspect. In one of the examples from before, someone came up with an example where the mortal would be effected, but not the wizard (I believe it was calling her boyfriend). If the wizard has nothing at stake and the mortal doesn't have an aspect dealing with the wizard then there doesn't seem to be any reason to have a compel there.

There is an exception here if you were to, say, compel the wizard to create that complication so that you can then compel an aspect on the mortal (like Easily Frustrated) to create a limitation on them. That way the wizard would be inconvenienced even though it wouldn't be directly.

Again though if there is no way the person with the aspect will be inconvenienced then, from a story perspective, why should there be a compel?