Feedback on Canon EF 70-300 IS f/4-5.6?

[sothoth]

If you go to Alaska and either miss shots or get only blurry shots because you didn't have the lens, you're going to kick yourself.

I'm going to borrow a Tamron 70-300 from a friend and try it out for a few days. If it seems like I can't get good photos without IS, I'll buy the Canon. I have a few months between now and Alaska to save up. I went to the best local shop in my area and tried the IS lens. I must say... it's impressive how it stabilizes noticably when you look through the viewfinder. I know IS isn't rocket science or anything, but I can see that it makes a big difference in everyday shooting, esp with a heavy tele lens on the end of a dSLR.

Thanks again for the advice.