A device wipe will reboot your BB to out of the box state, meaning everything on the phone will be GONE after you do it. Word of advice, if you remove any native app (Help or BB Maps for example) if won't come backafter the wipe.
Stuff stored on your media card will be safe.
If you're planning to wipe, use DM to backup your data.
Formatting the media card will erase the data and build a folder structure so that the BB can find it's way. Again, backup before you start.
After upgrading to a 4g (from a 2g) & using it for month or more I woke up today to find "A media card has been inserted that contains errors.To correct the errors please use a disk error checking utility on a computer."
After checking this site,I went to work>>>
I created a folder on my desktop,dragged all my media folders over from my open media card folder ,formatted my card via the scroll down menu option(which was pretty quick),then dragged my media folders back over into my now clean media card folder (this made even easiler & very nice since they're all in one folder),placed the card back into my phone & everything works fine.
Thanks to everyone in this forum.