i was asking myself similar question...i guess money is pretty strong issue
here. Of course L does better job. But, as far as i saw test shots of people
who already have 70-300 (NOT 75-300 one, but 70-300 USM IS), it's pretty
good. Also my first impressions having it are quite excellent. I guess
you've read my thread about exaggerating....well, i can tell you that shots
were taken seconds apart and i WAS shaking too damn much since i still felt
the thrill of having new lens... :-)) so, let's say that IS helps even at
worst situations...
But you can see many other test shots and all of them confirm usability of
IS. Of course, the best way is to buy a tripod...

You'll find a pretty good review of IS, and VR (as Nikon calls it), here:

http://www.kenrockwell.com/tech/image-stabilization.htm

Personally I do without it.  I use either a fast shutter speed when
possible, or a tripod when not.

Keep in mind IS only helps to compensate for camera shake, not subject
speed, or movement.  You also need to turn it off when using a tripod.  Some
swear by it, others swear at it.

Bill Crocker

I posted this one a while ago...

http://www.flickr.com/photos/10625820@N00/226588336/

f=200mm (300mm 35mm equiv), at 1/8 second.  I can't see any camera shake at
all.  IS/VR obviously works.

Hi Loopy,

I was in the same situation about six months back. My hands are pretty
shaky these days and I had used a series of Olympus (Uzi) and Lumix
ultrazooms with a fair amount of success.

Anyway, I finally decided that the time had come to change to a dslr and
chose Canon because of the IS lenses. (Yes, I now know that Nikon do
them too !)  Like you I had no idea how well the IS worked, unlike you I
was lucky enough to have a good shop locally who actually got in a
70-300 IS USM for me to try.  As soon as I stepped outside the shop and
pressed the shutter release half way the image stopped waving around and
snapped into rock solid focus. That decided me there and then to part
with the money.

Obviously, if you are unsteady on your feet it aint going to cope, but
I've found it to be a great boon.

I'd still recommend going for the maximum aperture you can though.

I could put up a picture of a robin taken at a ridiculous 1/15th sec..
But as you say, it don't really 'prove' anything.

Having had the 70-300 ( not 75-300 ) for six months I was becoming very
unhappy with the 300mm performance, it being decidedly soft to my eyes.
Even bolted down on a solid tripod..  It's currently with Canon as part
of the recall on these lenses, so things may be improved when it gets
back.  Never the less, I decided to blow the money and upgrade to the
100-400 L .  The first halfdozen pics I shot of a sparrow in our hedge
convinced me that it was money well spent.

If you can justify the outlay I'd say go for the 'L' grade glass, you're
unlikely to regret it.

Hi,
First, I won't buy another lens unless it is IS (or a specialty lens,
like tilt-shift).  My experience with IS ranges from 28mm to 500 mm f/4
L IS + TCs (sometimes stacked).  I am completely convinced IS works.
For long lens and action work, like 500mm +TCs, IS is important
even on a tripod.

I don't have any comparisons on my web site, but this is an example
of a 500 mm hand held shot:
http://www.clarkvision.com/galleries/gallery.bird/web/road.runner.c11.29.2005.JZ
3F5598.b-700.html
The guy with me had a 300 mm f/2.8 with no IS and got no usable
images, but I got sharp images down to the pixel even though
I was holding a larger lens giving more magnification.

If you want a good telephoto lens that gives sharp results, it is
my opinion that no zoom will work.  I started the cheap consumer
zoom route 20 years ago, and found the fixed focus lenses
delivered the performance and no zoom did, not even L glass zooms.
For example I have Canon 70-200, 100-300 IS, 100-400 L IS, sigma
170-500 (which is sharper than my 100-400 L), and finding
all these lenses lacking, I switched to fixed lenses and
now use 300 F/4 L IS and 500 F/4 L IS.

For high quality starter telephoto work, I recommend the 300 mm f/4 L IS.
Example image:
http://www.clarkvision.com/galleries/gallery.bird/web/lorikeet.c04.07.2005.JZ3F8
962.b-700.html
You can use a 1.4x TC and get 420mm f/5.6 and still have autofocus
with consumer DSLRs.  The lens is about $1100.

Roger
Photos at: http://www.clarkvision.com