Does it give an error when you try to unmount it? If so, what is the error?
I think you shouldn't worry too much about corrupting, if you are not using android.
If there is nothing writing to them and no pnds are running, it should be no problem to remove them.
No guarantee though.
As an aside, why are you running beta 5 and not the full release?
On the unmounting topic, if your cards are FAT formatted you shouldn't have to worry about unmounting. As mcobit said just make sure no read/write operations are happening when you eject. If your cards are Ext* formatted or multi partition, you do need to unmount properly. In any case you should install the latest firmware and see if the problem still exists (and check that thread for any similar reports).
I can't give you a sworn statement or anything. But in the all the time I've been using a Pandora, rotating through about a dozen SD cards and inserting/removing them countless times, I've never once had an issue. I only take this relaxed attitude towards FAT formatted cards though.i am using the full release, still have same problem. now, are you SURE nothing will get corrupted if i eject w/out unmounting? all my sdcards are FAT32 formatted. i'm just afraid it might mess things up. but if you and mcobit says its ok, then i'm gona do it.