For those that have yet to boot up MGO, expect to set aside some time for an update, though it doesn't seem to be nearly as long as the initial update for the beta. Maybe five minutes or so for me right now, so you may want to set that up when you first get the game just to get it out of the way. The release note says it lightens the strain the game puts on Konami's servers and adjusts your character'smoving speed. I think it also does an install, too, of about 550 MB, for those interested. It also does the "You must press the PS Button and select Quit Game to proceed." thing after you install the update.
Also, there's a song and octocamo to download in the extras portion of the main menu.
Edit: Concerning pricing for the MGO extra character slots, you have to go to the browser web page for this stuff and it's $6.99 per extra slot for up to three slots total, if I'm reading it correctly. You can also buy more voices, 32 additional voice tracks, for $4.99, which can be used on all characters under your GAME ID for free. That's so nice of them to do that.
How much do extra characters generally cost for MMO's? I've only played FFXI extensively, which I think was an extra $2 per character you wanted. If it were that cheap, I wouldn't mind getting an extra character or two, but for $21 for three more character, I don't see myself being eager to take them up on the offer. I remember the original MGO offered as many characters as you wanted for free, though that may have really been just free accounts to play with since you didn't really have a character.