[adam]

ooo! Thank you for the informative replies!
As for the useful range for me, I usually find that on my 18-55, for wide shots, I use 18, and for tele shots, I use 55, and usually wish for more. I think that I use the wide and tele ends more than I use 'in between'. Maybe I should go prime? But then as a walk-around lens, I don't really want to keep changing lenses.

This is important, because your SUBJECT might be moving and require a faster shutter - IS does not necessarily make this possible.

So, it's not possible to shoot using a fast shutter speed and use IS at the same time?
I guess that if I'm using a fast shutter speed, camera shake will not be as evident as compared to if I used a slow shutter speed, and if I'm using the slow shutter speed, with IS, and the subject moves, they will still blur, so I would have to use a faster shutter speed anyway, and with the faster shutter speed, won't see as much camera shake evident, so won't need IS when shooting with faster shutter speeds.
But the part I'm unsure about, is when you said that "IS does not necessarily make this possible", does that mean that I can not use a faster shutter speed when I'm using IS?

I'm starting to consider jumping to the 70-200 f/2.8L IS rather than getting a 70-200 f/4L. Getting the 70-200 f/2.8L will just mean that I skip the 70-200 f/4L, since I'll end up getting the 70-200 f/2.8L if I get the 70-200 f/4L, and that means that I'll be spending more money than necessary! So I'll just hold off buying for a little longer, and work some more to fund this purchase

At first, I wanted the 24-70 L lens, but the IS, cheaper price and larger range of the 17-85 is what's attractive. Surely the 24-70 should be sharper, especially wide open as compared to the 17-85.
Then after typing this, I start to think.... why walk around taking pictures that aren't sharp, but I convince myself that the 17-85 is 'good enough'. I'm just hoping that I won't convince myself that I need the 24-70 after I get the 17-85.

I think I better be safe and stick to the Canon lens, rather than the Sigma. Pay a bit more, and get something more reliable.

Then also, thinking to get it locally, at the shops here, but it's so much more expensive than if buying over the internet!! then again, if I pay a bit more (not really a bit, but a lot!), is it worth paying the extra money to get it locally? apart from supporting local businesses (who are also after my money). What do you think?