I like to play on anarchy servers alot, since it's pretty much single player, but with other people. When you join a server and most chunks are deserted of any natural mobs such as pigs, chickens, cows, you have to resort to farming. Now, farming can take a few minecraft days, and by time it hits night, your hunger bar is already at 4-3 chicken legs. You have to go out and get bones (killing skeles), then planting the seeds and harvesting them to make bread. Now add in the challenge of factions with diamond swords and iron armor sititng at spawn waiting for you to leave the non-pvp zone, with the ambushes, and ect.
Hunger really does add in a challenge, and pressures the player as in "hey bro, you gonna starve and die, better get some food".
I had to resort to eating zombie flesh for a few nights because of the insane lack of peaceful mobs and huge desert biomes. It's actually fun to play minecraft now.