We're just back from a 4 day trip -- 2 1/2 days spent at the parks. We spent the day on Friday with a friend and then went to DL park from 6 until about closing. We knocked out so many "big" rides (Pirates, Indiana Jones, Jungle Cruise, etc.) that night -- with almost no waits -- 10 minutes, max. Saturday we spent at DL all day -- got there right at opening time. Sunday we went to CA, but went to DL park from 8:00 to 10:00 to finish up the things in Fantasyland that we didn't get to the previous day due to really long lines. I would definitely recommend going to Fantasyland in the morning -- we rode everything in 2 hours. We got through CA in one day -- seeing almost everything (that adults would want to see -- this was a no-kids anniversary trip)and riding most things. Monday we went to CA to ride Soarin' again (my favorite) and then we spent some time shopping at DD and DL park.
We didn't feel like we missed anything -- one of the nice things about DL. You would miss a lot at WDW if you only had 3 days.
Have a great time!