I successfully installed magiclantern-2010Dec20.550d.fw109.iso+menu.alex yesterday on my 550D (nice job!). The firmware works with 2 different SD cards that I tried (after making the cards bootable). The problem is that it doesn't work at all with my Eye-fi Pro X2 cards. I have tried both bootable (with the autoexec.bin file on the card) and non-bootable. In both cases the 550D doesn't appear to power up - but it does come up partially... Interesting - no screen, black, pressing DISP, Menue etc has no effect. But, pressing shutter causes the lens to autofocus! No picture is taken. I need to remove and reinsert the battery to get back to normal. One more question - is there a version/varient of the magiclantern.fir file that undoes the camera changes - in other words, resets the BOOTDISK flag in nvram. I want to try from scartch again (and also attempt to get my Eye-Fi back!!!).