If you have a 1.0 account, you get two weeks of free play that starts at launch. If you pre-order any version of the game, you can apply the pre-order code to you 1.0 account for early access and the bonus items, but you can only apply the full-game PS3 registration code to your 1.0 service account.
If you add the PS3 game code to your existing service account, you will get 30 days, and those days will start after the 2 weeks of the welcome back campaign. If you pre-order the PC version, you can either give away the game to someone, or add a second service account to your SE account but those service accounts don't share characters so it's only good if you intend to dual box and maintain two monthly fees.
Additionally, if your 1.0 account is a collector's edition, you will automatically get by mogmail the 2.0 collector items, without having to do anything. You will not receive the pre-order items unless you pre-order, or get into early play.
Well, I'm not sure if that's less or more confusing, after all