Created a quick app to re-mount the microSD card as read/write for rooted Motorola XOOM Honeycomb 3.2 users. This app simply dismounts and remounts the microSD card in its "stock" location as read/write. Optionally, you can also add a mount point to /sdcard/external (which is friendlier for some apps).
I hope this helps some people out, I know I like it.
APK Download V0.1b
** FIXED Force Close when /sdcard/external folder doesn't exist **
BTW: I don't have enough posts to put this in development, where it belongs. Mods - Feel free to move this thread as appropriate.
edit: This app is still under development, use of this app is at your own risk. The app will forcefully dismount/remount the sdcard, so any active access to the sdcard is affected, and under extreme cases can result in data loss.
I'm adding a lot more error checking, validation to minimize any chances of data loss. Also, I'm working on hot-swap sdcard support, remount-on-boot support, and a widget to easily get sdcard status.