This needs a public-facing page for everyone's votes (wait a minute…). Let them see and interact before allowing access. Right now, nobody will use it because the splash page gives no indication of what the actual application is like or how much activity is behind the login wall.
I agree that a screenshot of some sort would be nice even if it is just generic links posted by celebrities and the such. Another interesting feature to implement if it isn't already (I don't use twitter so I can't really try this out) would be to use a similar system to digg/delicious/hackernews/reddit in showing how many people have posted a certain link (i.e. upvoted) or having the ability to sort by popularity of links
