Yes, you can have multiple accounts per console. And because it's free, I would think (based on a small sample, my friends who own PS3s), it's far more likely that there will be multiple PSN accounts, versus XBL accounts which cost money (to play online).

My PS3 has three PSN accounts on it, do three or four of my friends'. Everybody I know who has a 360 shares one Live account across everybody who uses the console.