Hmm. Alright, yeah, I'm getting a better picture of what you mean, Accord. I'll freely admit that after the "diseases" comment, I was seeing you as an arrogant GM who thought his ideas were [i]so[/i] great that no one could [i]possibly[/i] get bored with them... I'm sorry for misinterpreting.

Honestly, though, I do think these people should be cut a little slack. Like Prince said, no one is ever going to learn their style and the RPs that best fit them if they're constantly rejected from everything they want to try... Dealing with that sometimes inevitable disappointment is another integral part of GMing. Over time, some people just aren't going to click with you, or your style, or with the group, and when they don't click, they don't have fun. When they don't have fun, the RP (no matter how excited they were at the beginning) is suddenly a [i]chore[/i], and they're stuck. They feel like they have some responsibility to stay and muscle through it, and they know that the GM and the group would probably be very frustrated if they just left (-cough cough-)... And that's where the excuses come in. They tell themselves, and the GM, that they'll "work on a post soon" or that they "just need some time to work out a character thing", or whatever, when they know they probably won't have the motivation to actually follow through.

My point is, guilting people into continuing an RP (something that is quite time consuming, and done for entertainment) when they [i]really[/i] don't want to is futile, and even rather a bit cruel. The GM in this situation needs to accept the disappointment, accept the frustration and simply move on. Sometimes that person was absolutely integral to the plot, and their leaving ruins the entire game. That [i]sucks[/i], and if that happened to me, bitching would indeed be the response, but even then, you [i]move on[/i]. You make new RPs. You talk to the other people in the group, and see if you can get it restarted, see if you can work around the absence.

Sometimes it's frustrating, sometimes it might even bring you to tears, but that's the job. Players are just people, widely varied and always changeable, and unless you always play with people you've known for years (and every once in a while, [i]especially[/i] if that is the case), you aren't going to get perfect players every time. You're going to get disappointed, and you have to work through it.

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EDIT: Funnily enough, this very thing happened with me a while back, in a game that Lillian was running (:sun I like the new avi/sig, by the way). [i]I[/i] was the player, the person who loved the setting, loved the plot, made a character who I thought could be quite interesting to play, and even started off a bit of early drama with the villains... And then it just lost me. Hours I spent, trying to write a good post, trying to contribute to the story, and it wouldn't come. I was actually even brought to tears just writing Lillain a PM about how much trouble I was having, that's how emotional it was. I was [i]so[/i] ashamed, so angry at myself. I was in an RP with [i]Lillian goddamn Thorne[/i], and I was fucking it up. Jesus, that sucked so much...

I ended up killing the character off there at the beginning, and that was that. I was out, and I felt a thousand times more free, even if I was disappointed in how poorly I had handled it. In the end, the most healthy thing to do was just to leave. 

I realize this isn't exactly an equivalent situation to the "boredom", but I thought it would be good to bring it up.

EDIT 2: Oops, I forgot to mention that Lillian was very understanding, and handled the situation as I think a good GM should. :) She helped to provide an interesting exit, I left the game, and there was no bad blood between us or anything like that.