Sorry for stating what could be the bleedin' obvious here but... I presume that this is going to use your iTunes account the same way the iOS app store does? Personally I really hope that's the case as I usually pick up a load of iTunes gift cards whenever there's a buy one, get one half price deal on so that'll be (effectively) a nice discount on my software going forward.
This is going to be very interesting to watch develop, especially with the January 6th launch date. Considering Microsoft are rumoured to be showing off Windows 8 at CES at a pre-show January 5th keynote and that an app store is rumoured to be a key part of Windows 8 (and kinda vital if that's the OS they're going to be pushing tablets with) they're effectively going to be giving Apple a load of free publicity. "Microsoft push App Store as the future of Windows in a year's time... and here's Apple's version live now".
)