I usually don't comment on wild Apple rumors, but this one is so crazy that it deserves hitting with a spiky bat.
Which rumor am I talking about? It's the "iPad 2 will have Light Peak" nonsense.
Why is it nonsense? Well, ask yourself this - what are iPad 2 owners going to connect to this said Light Peak port? All that exists of Light Peak so far are prototypes that use hybrid USB 3.0 connectors. No current hardware ships with Light Peak support, so why would Apple stick a separate port (on the top of the iPad 2!!!) for something that just won't see any usage? Not only would this port be redundant on a device that will ship this April, but one that's also in a totally illogical, awkward, and ugly spot.
It makes so little sense for the iPad 2 to have a Light Peak port that I'm surprised at MacRumors even running the story. Perhaps it was a slow news day?
Equally, a Mini DisplayPort doesn't make much sense either. Why would Apple stick a port for this when AirPlay does the job?
[UPDATE: I agree with Cult of Mac - it's most likely a SIM card slot. A regular old boring SIM card slot.]