There's still no release date for the Castle Crashers port to the PlayStation Network, other than "hopefully sometime this year". The Behemoth really seems to be polishing this game up for PSN users, in addition to developing a brand new game for the Xbox Live Arcade.
To make the experience more unique, The Behemoth is adding in new content, the most prevalent of which is a volleyball minigame (you may remember this being used as an ending sequence to one of the campaign desert levels). By their account, volleyball can be played online or locally (or a combination), 8 vs 8 or 4-player co-op.
Here is the official feature report:
Play co-op or vs your buddies
Local or online play
From 1-4 players per team for up to 8 player matches
Variable stats based on character
Use magic attacks to place 8 new magic status effects on the volleyball
Cool new serving and spiking moves
Available AI teammates or opponents
Play as any character you have unlocked
Play 1, 3 or 5 matches against your opponents
Leaderboards to track the best in the land
It’s basically like playing volleyball with your friends but you get to replace good sportsmanship with explosions, magic, and weaponry.