We were at the Magic Kingdom last year on MLK day. We arrived around 12:30 pm and had no problem at all with the attractions in Adventureland. But the MK was very crowded. MLK day was one of only 2 days when SpectroMagic was performing, so the park got VERY crowded in the later afternoon. In talking with people as we waited, they said that the MK was extremely crowded that weekend. It's still very doable, though, if you have a touring plan and know what you want to see and when.