| Re: 70-200 2.8 Should I buy? Reliability seems ??
Replying to things out of order...
>I remember the IS motor always seeming to take longer to allow the lense to lock on to focus.
I don't think the IS slows the focus at all. Focus speed with a given lens is a function of available light, and the patterns/contrast underneath the focus sensor, and which camera body you have. The USM is the same in the IS and non-IS version of the lens and the aperture is the same so the camera is getting the same light and reacting the same.
I use IS on mine when I'm doing candid shots and when I'm shooting something I'd normally use a tripod for, but I don't have it with me, such as nature/landscapes. The last time I did that it was to get some shots of cactus flowers; I couldn't get the tripod where I wanted the shot, so I used the IS to steady the lens-shake.
>About how slow of a shutter speed can you shoot at 2.8 with the non IS version?
Canon's IS and Nikon's VR are marketed in a way that fools or misleads people. They make it seem like it'll provide a blur free photo when a non IS or non-VR lens would blur. That's not entirely true. There are two movements that can cause blur in a photo and the IS can only help cure one of them within a certain range of settings.
Say you're shooting and the available light is forcing f2.8 and you're at 1/200 second. The guideline for reducing the blur from hand-held motion says that 1/200 should be fast enough to eliminate most hand-motion blur. Now, you decide you want more depth of field so you roll the aperture to f8. You're about 1/50 now, which would be way below the guideline's recommendation, but IS will help compensate and you'll have a good chance of getting that shot.
If the subject moves though, 1/50 is 10x below the needed 1/500 second recommended to stop SUBJECT blur, as is the 1/200, and IS is not going to help.
Or, if the light levels drop further, or you need to add more depth of field, and your shutter speed drops to 1/25, you're outside the range of the lens to counter movement so you'll need to do something else (like rest the camera on something or fire several frames hoping one occurs when you're not moving the camera. And, once again, IS won't be helping because you could do the same things with a non-IS lens.
>So I primarily would use this for skateboarding, snowboarding, motocross, extreme sports, etc. [...]
> What kind of stuff do you typically shoot??
IS also gets in the way shooting sports where the subject moves erratically. I'm a pro-rodeo photographer, which means my action can be anything but predictable. IS wants predictable motion such as panning, where the IS can compensate for the movement 90 degrees to the pan providing a nice smooth linear blur, or it wants no panning but very slight wobbles as we try to hold still to shoot a motionless or very slow moving subject.
When you shoot something weaving back and forth, like a football player moving through a defensive line, or a basketball player going in for a lay-up, or a motocross rider weaving through ruts, then your lens will think it should try to stabilize the motion and will end up causing the lens elements to be behind the subject. Then it'll hit the end of its ability to compensate and have to reset and start stabilizing again. And as it does that it'll jump, and, for whatever reason, that'll be when you're firing so the shot will be off.
Don't get me wrong, I think IS is great. It's not the cure to all blurring problems though. It is great in the right circumstances, and I'm glad I have a lens with it for those times it works. However, as far as what I do the majority of the time it doesn't help at all.
One time I appreciate it a lot though, is when I put on my 2x tele-converter. Then the 70-200 is a 140-400, and IS helps make those 1/400 speed shots easier. It compensates for those 2 stops of light lost to the 2x but I still have a nice sharp zoom that is easy to carry.  | 
Linear Mode
