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Well, it depends on your ability to hold a camera.  If you are always
using a tripod, you are always in very bright light, or you can accept the
noise (grain) at the higher ISO, then you may be able to manage without.
Having now used a camera with IS (the Panasonic FZ5), which gives you
about three stops gain in shutter speed (i.e. you can hand hold the 432mm
zoom setting at about 1/50s) there is no way I would wish to revert.  Why
not try it and see for yourself?

David

You should test and decide for yourself.  I took my camera,
which has no image stabilization, and zoomed up to 10x, which is
roughly equivalent to a 280mm lens on a 35mm camera.  I took
a series of photos of a calendar from about three feet away.  I
took five photos each at shutter speeds from 1/10s to 1/100s,
resting between sets.

I then dumped the photos to my computer and examined them.  I found
that I couldn't reliably handhold below 1/80s, with "reliably"
defined as 4 out of 5 shots without visible shake.

The 1/80s limitation means that shooting outdoors during the day
should pose no problems throughout the zoom range using low ISO
levels.  Indoors however, forget about handholding while using
the long end of the zoom for candid long range shots.  There will
never be enough ambient light to shoot at 1/80s unless high ISO
levels are used and then there will be a lot of noise in the
photos.