IS is so much better than f/2.8 for landscape stuff, f/2.8 isn't much DOF. f/4.5-5.6 and IS does soooo much more.
When I started shooting macro, I had to realize how many things in the natural world actually move a tiny bit, I never realized until I tried longer exposure times. Often the same applies to landscape, IS doesn't freeze leaves from jiggling or water from waving. In this case, neither shallow dof *or* IS will help, what's really required is a high iso high dr camera which Canon doesn't have yet.
True, but a little water blur and even some leaf blur from a single shot isn't always so bad and it's not like IS gives you 10 stops to where you are holding really long exposures.
There are lots of times where you don't want to bother with a tripod or can't.
I nabbed an f/9, 50mm at 1/20th the other day with IS in a deep forest and only had to go to ISO400 (i.e. right before the table starts falling out for Canon DR (of course with Nikon I'd had already traded away two stops, maybe Canon is better, I didn't lose two stops going ISO100 to ISO400