The XOOM's currently nonfunctional microSD card slot has likely turned off many a potential buyer, but – if you're willing to take your chances with unofficial software from the Android dev community – the problem has finally been solved.
The solution comes by way of an update to Tiamat, a custom kernel from XDA member bigrushdog. Installation is more or less identical to any other kernel, but if you need instructions, knock yourself out:
1. Reboot into the bootloader by running:
adb reboot bootloader
2. Flash the boot image to your boot partition, then boot back into Android by running:
fastboot flash boot boot.img
3. Push the bcm4329.ko, scsi_wait_scan.ko, and any other modules to your /system/lib/modules folder and reboot.
adb push bcm4329.ko /system/lib/modules/bcm4329.ko
adb push tun.ko /system/lib/modules/tun.ko
adb push scsi_wait_scan.ko /system/lib/modules/scsi_wait_scan.ko
adb push cifs.ko /system/lib/modules/cifs.ko
adb push vold.fstab /system/etc/vold.fstab
As bigrushdog notes, the contents of the SD card are contained in the "sdcard2" folder (not the "sdcard" repository). Other than that, the procedure seems to be relatively straightforward – if you're interested, hit up the source link to get started.