I think it'll be 'as you are'. The release itself will generate enough press, so they don't need a software update at the same time that gets lost in negative press about re-locking etc. Also, they won't offer anything which favours Apple Stores, as they're also selling through O2 stores and CPW. So I think the phone itself will be the surprise.
Why would Apple gives us a £50 store credit, the yanks got $100 credit because Apple slashed the price of the iPhone by $200 and it outraged thousands of customers.
Apple haven't done anything to us (yet)
Very unlikely that they're going to release an update on the day that includes MMS or Video Recording, but, I have a sneaky feeling Apple has all these things ready to release whenever they feel the 'need' to.
What better way to keep your customers coming back for more of what they need? Deprive them of the necessary things in the first place. Apple needs us to upgrade for some unbeknown reason.. Stick in a major piece of software we're all craving and bang, we won't be able to connect to iTunes quick enough to get our hands on it.
They will surprise us by not giving us a mains adapter because the UK one is bigger than the US one so it doesn't fit in the box. Or maybe give us a funky little stand like you get with the iPod Touch - ooooooh I hope so!!