I was having the the issue where the delegate options were all greyed out and I couldn't change them. We are now using Office 2010 and the issue is still there. I played around with it and I have found a solution to change the greyed out options.

I went into the delegate options and this particular user has about 10 delegates that are ALL only reviewers to the calendar. I went into the permissions of one of the users (it didn't matter which one) made them and EDITOR of this persons calendar and then checked off the checkbox that reads "Delegate recieves a copy of meeting-related messages sent to me". Once I OK'd out of that permissions window the delegate options were then available. I change the default setting (which was My Delegates Only) to the recommended setting. I then went back into the user I made and editor and put them back to reviewer. When I OK'd out of that window again, all the settings were greyed out again but my changes had stayed on the recommended setting. BAM

Enjoy