Nathan Drake's next adventure will feature some kind of multiplayer action, and you'll get a chance to try it out in the near future.
Uncharted was a completely singleplayer affair, with you and only you guiding lovable protagonist (and totally dreamy) Nathan Drake through his adventures. Uncharted 2: Among Thieves, on the other hand, is no solo outfit: it'll feature some kind of multiplayer, though details are decidedly sketchy about what form that multiplayer will take.
What we do know, however, is that you'll be able to find out for yourself soon enough. The news of the multiplayer mode was revealed by way of a picture of placeholder box for Infamous that'll be used to promote pre-orders at Best Buy stores. The box advertises that when you pre-order a copy of Infamous, you'll receive not only a downloadable demo, but a "multiplayer beta voucher" for Uncharted 2: Among Thieves.
Meanwhile, rumors of a possibly co-op mode originally reported on by Screw Attack remain unconfirmed. Screw Attack's source described the co-op as being more than just the singleplayer campaign with an extra person, which does sound pretty intriguing. In any case, there's your reason to pre-order Infamous.