Finish your pictures. I tend to go on deleting sprees during my free time (and I assure you that I have plenty of free time).
To prevent incompleted pictures from being deleted:
1. Finish them in a reasonable amount of time.
2. Set them as unfinished hidden if you don't plan on finishing soon.
3. Remember to set a picture from unfinished to finished when you're done.
4. Check if you have any unfinished work. (Hint: Intermediate Boards..)

And that's all.. well.. that's not all, but that's all for now. ;x

More like word to the unwise.

Not really. I want the wise to stay. And for the unwise.. well, there's the damn door they'll be shoved through.