We actually did 3 CM's on our last trip in May 2004. We did the Pooh & Friends Breakfast at Crystal Palace in the Magic Kingdom, Chef Mickey at the Contemporary, and the Ice Cream Social at the Garden Grill.
Out of all 3 of those....my son interacted the most during the Ice Cream Social. The times for the ICS are usually from about 2:30 to 3:15. We had the last seating (3:15).
By the time we sat down, the place was practically empty. My son was able to take a picture with all the characters. Mickey came "play" with him for awhile. My son showed Mickey how he can write his own name...etc. Then, Pluto and Chip came to the table at the same time and stayed for a good 5 minutes.
I would suggest an early lunch (like 11am'ish) so that you can work up a good appetite for the Ice Cream. The price was $8.99 for adults and a couple dollars cheaper for kids ($6.99?).
You can then have a late supper that night and eat cheap to make up for the cost of the Ice Cream Social. I've also read that people in your party that do not want the ice cream can pay $5 per person to sit with the party, but not eat....I don't know if that's accurate.
We were also able to order drinks with the Ice Cream which we were not charged for (included in the price).
Finally....I found that the Crystal Palace buffet was good...but, we didn't care much for the actual food at Chef Mickey's.
This year....I've been giving my 5 year old a $2 per week allowance. He's saving to pay for breakfast for all 3 of us and souveniers. He also received $40 worth of Disney Dollars from various relatives for Christmas and he now has over $120 saved for the trip.
If you want to do the Ice Cream Social...make sure to make a Priority Seating arrangement in advance. I called about 2 months before our arrival and everything was booked up until our last day since there are only 3 seating times per day (2:45, 3:00, 3:15).
Hope this helps....
speed