I am also booked for that week, arriving the Friday (April 25th) at the end of Easter week. From what I have gathered there will be pretty big crowds that Friday to Sunday (more's the fun, going early, ducking crowds and feeling accomplished) but then it appears that there are very little afterwards. That Monday I am planning a really fun day at the parks.
My girlfriend has never been and so it will be hard to keep her from wanting to stand in huge lines when we arrive, and I'm sure that we will, but I also think she'll really enjoy the difference between when we arrive and when those week days start. I have never seen Disney when it's less crowded..... Of course my parents were never the best at planning a vacation (when we went in 1986) so we tried a lot of very popular rides in the middle of the day. I am a wizard at planning Disney world now so I am pretty sure that we won't spend a lot of time waiting for rides.....
At any rate from what I can gather the crowds will be dying that weekend (25-27th) and then will be pretty mellow afterwards.