Instructions for 3.8 are different for a vfat partitioned disk

The uEnv.txt instructions are slightly wrong if you use a vfat partition (as is shipped).

...
devtree=/boot/am335x-bone.dtb
dtboot=run mmcargs; fatload mmc ${mmcdev}:1 ${loadaddr} ${bootfile} ; fatload mmc ${mmcdev}:1 ${fdtaddr} ${devtree} ; bootm ${loadaddr} - ${fdtaddr}
uenvcmd=run dtboot
optargs=consoleblank=0
..

Might be worth noting that you can check out and use u-boot from master/v2013.01.01 as well.

Hope this helps.