I am using VM fusion to run my Windows 7 Home Premium boot camp. If I boot from windows "boot camp" it shows the sd and it shows it on osx lion. But if i run vm fusion the sd card is not visible. I didn't know if it was a setting or a common problem. The weird thing is on my 2010 MBP it shows.
If your VM has its own window there is a USB icon in the lower right border of the VM window. Otherwise, find your way to the VMWare Fusion menu bar and select Virtual Machine -> USB -> Connect <SD card reader>
This has been discussed on VMware's forms. If seems that Fusion has an issue with the card reader and will need an update for this and other issues with the Retinabook. Also has some issues with screen resolutions and I am sure some others.
Stay tuned. I am sure they will get an update out soon.
I don't know if Fusion supports it, but have you tried drag and drop your SD card from the Desktop to the Windows Desktop?
I couldn't mount mine on my Parallels 7,
so I tried and Dragged it, worked seamlessly just made a shortcut Folder to the SD Card.
and I don't think that the SD card slot is an USB Device, since it is faster than USB 2?