I keep saying that I got mine for $850, and it was a fairly new (2006 or 2008) copy; complete and in great shape. No regrets whatsoever.
If Canon were to release a new model, I'd probably not bother picking it up unless it was demonstrated to have some useful improvement, like an even shorter minimum focus distance, markedly better microcontrast at f/2 (as noted, this is already one of the best lenses, so that would be really something) and IS. As it stands, you get a lot of value from the lens, and it is about as wide aperture as a lens can be while still being useful for low-light applications on the current crop of DSLRs.
Out of Canon's entire lineup of older designs, this is one that stands out as being worthy of a purchase without any thought to possible future improvements.