I would assume the OnLive group.  If it is an issue on this forum, I am sure it is an issue for others as well.  Mods could only help the service, so they would have to determine if the costs were acceptable to increase their appeal.  If they automated it well enough, and their cloud service infrastructure was scalable enough, it would not incur too many additional costs after the initial development.

You could be right, but I can see some roadblocks due to security problems... A rogue mod with some bad code (like a virus or simply software bugs) could cause chaos at Onlive's servers, unless they only allow the most basic mods (like changing models or some interpreted scripts).

I'm just skeptical that mods will be simple and free in this kind of environment, retaining all the aspects of the present mod community.

Yeah, there would definitely be some hurdles.  It would be much harder than deploying XNA content because XNA is all based around the same framework.  There can be no limitations for such a broad service such as this.  But your concerns are basically the same concerns for all cloud services.

Also, I am wondering how the cost to developers are going to be.  Is it a one time fee to get your game on the service?  Is it based on bandwidth usage and cpu usage?  These OnLive guys better have one hell of a cloud for this thing to work right.

You're right, I don't see them charging the same for all the games. Surely they want to encourage developers to optimize their games in order to minimize costs.

The question is who pays the difference, developers or gamers.

i think it might.