Just two cents from a user's point of view (someone viewing not uploading the slides). I think the interface is very pretty, but it lacks a few features that seem essential to me. First, you can only advance or go back one slide at a time. There's no easy way to jump to a specific slide if you want to go back or forward and review something. Second, there's no download option. (From the point of view of some uploaders and SpeakerDeck, this may be a feature not a lack of one.)

I understand that it's still in beta, so this isn't a major complaint, but I would love to see these features added.