It is a topic often discussed so I thought I would comment on my experience. We went on 12/22 and it rained all morning (till around 12:30 pm). We came prepared with ponchos and umbrellas and found these helped a lot. We stayed relatively dry, as long as we avoided puddles. Our mistake was going on Splash Mountain which proceeded to get our shoes/socks drenched. There were more people there than I expected (even with the rain) and the park itself seemed busy (not surprising given the Holiday period). However, the rides themselves had short lines. The longest we waited was 20-25 minutes and that was for Nemo. We did all the rides we wanted by 1:30 pm (see below) and then shopped and left. It was totally worth it to us, given this was the only day we could go. That said, I'm glad my daughter stayed with the grandparents and did not join us. Young children (under 4 years old) seemed to be having a miserable time in the rain.
Space M (2 times)
Buzz
Star T
Nemo
P Pan
Snow W
Pinoc
Indy
HM
Pirates
Splash M
Winnie
Matterhorn
Space M (2 times)
Buzz
Star T
Nemo
P Pan
Snow W
Pinoc
Indy
HM
Pirates
Splash M
Winnie
Matterhorn