Photo.net have taken a look at Image-Stablised (IS) lenses, specifically from Canon, and investigated if they really do offer any advantages over normal, non-stablised lenses.
“One of the most popular question on web forums is some variation on “what should I buy” or “Is it worth it”. This article addresses some aspects of the issues of which 300mm lens to buy and whether IS is worth it! Is it worth an extra $200 to upgrade from a Canon EF75-300/4-5.6 lens to the EF75-300/4-5.6 IS version? Is it worth the extra $400 to upgrade the EF75-300/4-5.6 IS to an EF 300/4L (used, since it’s not made anymore) or $700 to upgrade to a 300/4L IS lens?”