12800 I get what you're saying and without a doubt it can be useful for a select few situations. I typically don't run that slow of a shutter to avoid subect movement, not mine. I once went to Pioneer Square in Portland OR and was told by a security officer that I couldn't use my tripod because it was considered erecting a structure.
When I was at the two museums, my most-used shutter speed was 1/6th, and I rarely went above 1/20th. Without IS, that wouldn't have been possible. My worst situation was 0.6 seconds at ISO 3200 and f/4 pushed two stops. That's a dark environment! I still got a solid, sharp shot. I wouldn't have minded having f/2.8 on that one because DOF wasn't a problem.
Generally, I find f/2.8 lenses are too slow when I have moving subjects in poor light. That's when I use the primes. Just the other day I was again shooting at ISO 3200 and f/1.8 at a wedding. So I consider an f/2.8 lens to be a lens primarily for stationary subjects where the IS is really helpful, or as a slow zoom where I'm going to add flash or I have good light anyway.
But oh well, I'll just keep my 24-105.