I have a 64GB MicroSDXC Card that was originally formatted to ExFat. I originally tried using the SD Formatter from the SD Card Association to format to FAT32. However, it would only format my card to ExFat. I was since able to format my card using Diskutility on Mac OS X Mavericks. I formatted it to FAT (that's what the selection specified), and erased all data. I then imaged the card using dd.
When I power on the Pi, both lights turn on and remain on. I haven't noticed any flickering, even during the supposed boot up. From what I understand, there should be some flickering of the green light while it is booting up. This has not been the case. Furthermore, absolutely nothing shows up on the monitor.
It seems to me that the problem is with the Pi not booting up. I spent hours today re-formatting and making sure that there weren't any extra partitions, and that everything was getting zeroed on the card. I'm not sure what I'm doing wrong.
One thing to note is that, after I formatted the card, it showed up as FAT32 when I checked the properties. After imaging it, though, it showed up as FAT16 in properties. Also, I'm using the latest download of Raspbian from the raspberry pi site. I'm not using NOOBS, and instead have directly imaged the raspbian wheezy image onto my microsd card.