I've noticed a problem on the two SMP servers i play on (LegendsUnleashed and ProspectCraft). Since the upgrade to 1.04 I'm not seeing mobs spawn at night. First couple of nights I was just thankful I didn't have to deal with any surprises when I climbed down from my little tower to get to work. After that it just seemed too quiet. Legends is on normal difficulty, and Prospect on hard. I've been just leaving my character up at night in the open. Saw a zombie one night, other nights no mobs at all, normal or lycanite. A trip to the nether saw one pigman. Bother servers are pretty deserted and I'm generally the only player on. For the nights I've tested, it was just me loading chunks in the world.