So I was playing with Ringdroid today and somehow managed to corrupt my SD card.
I was trying to take some very precise snippets of songs and noticed that the starting and ending counters give them impression that they can be stopped arbitrarily precisely (at least to the thousandth of a second). So I created a few ringtones and saved over them with the same names and deleted and resaved them, etc. trying to get exactly the right starting and stopping points and when it was all said and done my Droid gave me a "SD card is damaged" (or similar) warning and asked me to reformat.
I don't know exactly what portion of what I was doing caused it to freak out, but I can't imagine that trying to edit an MP3 down with that level is precision is even possible with such a simple program, so maybe that was part of the trouble. Maybe deleting and re-creating ringtones with the same file names was the trouble. Who knows.
I was able to put the SD card in a card reader (I was bummed to find out it's only Class 2, so I'll be swapping it out with the Class 6 from my G1 at some point) and save almost all the files by backing them up one or two folders at a time onto my PC and then reformatting and copying it back to the card, but it was annoying enough that I'll be more careful using Ringdroid in the future and I recommend that others use it with some caution as well.