If you try your phone card, back it up first. I am not sure which action wiped my phone's microSD card, but it's now blank.

It only had apps on there, no real data so I can just take the time to put them back on.. but....
Here are the steps i was playing with and I am not sure which one wiped it.
1. Inserted card in to microSD card adapter to check which file system it was (FAT or NTFS.. it was FAT32
2. When windows read it, it said it was not formatted properly and asked if I wanted to. I said 'NO'.
3. Then tried it in the MicroSD slot of the Xoom (for grins and giggles.. nothing)
4. Then accessed it through the host cable - didn't see anything on the drive so I thought it wasn't reading it properly.
5. Put it back in my phone.. phone said it was a blank card.
Oh well.. life moves on and another lessoned learned the hard way. The downside of experimenting.
Also, I tried a Toshiba 500G external drive (has only 1 miniUSB port but came with a dualUSB y-split port cable.. one for transferring and one for charging)... and the xoom didn't see any of the files on it. So I think it needed more power.. but I didn't go further as this one wasn't backed up yet and I didn't want to test my luck after the microSD incident.