The 70200f4 is undoubtedly a fine lens. But with the introduction of the new 70300IS consumers now have an alternative that rivals it optically and gives you other perks lacking in the L. Things like build, real USM/FTM, and AF speed are innate to the L, and the new 70300IS doesn't give you that. But optically speaking, this 70300IS has gone to a new level than its predecessor could never even dream of. The more I use it myself the more I like it. It really grows on you. Klaus over at photozone did a fine review and his conclusion almost mirrors my own [Italics mine]:
"The performance of the Canon EF 70-300mm f/4-5.6 USM IS came as a total surprise. Unlike its predecessor the lens is capable to produce a very high performance throughout the zoom range without the significant drop in quality at 300mm typical for most consumer grade lenses in this range. It seems as if the new UD element helps to lift the optical quality significantly. Distortions, CAs as well as vignetting are also very respectable. So in terms of optical quality the EF 70-300mm IS can be almost described as a hidden Canon L lens. As much as it may promise here its build quality remains in line to what you can expect from a consumer grade lens and the small max. aperture is limiting its scope specifically regarding portraits where you seek for a pronounced fore-/background blurr only possible via large apertures (f/2.8 and larger). However, if you're looking for a very good, light-weight tele zoom e.g. for travel photography this lens should be high on your shopping list."
Here's the entire review: http://www.photozone.de …non_70300_456is/index.htm
It's definitely worthy of consideration, at the very least.
