I want to do a Glacier walk in Juneau!
I haven't booked my Alaska cruise but am planning on booking soon! i just can't decide between May or August!!
I agree with Nancy (Hi Nancy!!!)
My family went on an Alaska cruise with Princess (couldn't wait for Disney) and we booked all of our excursions independently. It was easy and cheaper than the cruiseline excursions. Met lots of folks on Tripadvisor and Cruisecritic who were on the same excursions.
UMTerp

Hi, Brenda!
I met Brenda on Cruise Critic, and later in person at the Denali Lakeview Inn in Healy (near Denali National Park) where we both stayed in August 2008. We also ran into each other at Homewood Suites in Anchorage.
I was on the Coral Princess in June 2007, HAL Veendam in July 2008, Golden Princess in May 2009, and I'm going to Europe next week!Hey, DH and I were in Alaska in August, 2008, too! We traveled with Princess though so we were in the Princess lodges and Captain Cook in Anchorage. We are going again with DCL in August, 2011.
I'll be on a 14-night roundtrip on HAL Amsterdam from Seattle in August 2011. 
Helicopter glacier excursions are more likely to be cancelled in August than in May.
I've read it's because the summer heat melts some of the ice - especially by late August. Fog will also ground a flight.Would this be because of fog or some other reason for August? We are going in August 2011 and this is one thing I would like to do up there.
Don't wait until DCL announces their excursions, but do your homework and learn about the Alaskan ports now. There are lots of Alaska guide books at your library. I recommend Frommer's Alaska by Charles Wohlforth and Alaska By Cruise Ship by Anne Vipond. The Alaska ports of call board at Cruise Critic will also be helpful: http://boards.cruisecritic.com/forumdisplay.php?f=55