Ah, but in this implementation, clicking on the new content doesn't make it go away. It's really not intuitive for a first time user (like me for instance).

We actually used this effect inside of Twiddla for a while, with universally bad user response. Ditched it in favor of boring lightbox-style pseudo popups.

I just tried out Twiddla, it's really cool, congrats.

As per this slide-in UI, I'm going to change my mind here and say you're right. It really is kind of pointless... it's the same thing as a lightbox, only vertical, and more disruptive and disorienting.

I do think there could be some use for it... maybe someone will make a twitter app that uses it.. twitslide perhaps.. and we can all be amazed that they did it in x hours just as a side project.