There's a bug in nano (and pico, as pico is just symlinked to nano) in 10.4 (including 10.4.4), which can seemingly cause you to lose the document you are working on.
If you have an open document in pico, and then resize the Terminal window to get more space, pico should resize to fill the terminal. Instead, all of the text you're editing, along with pico's interface simply disappears!
For me, this meant a lost shell script first time round, and a search on Google found no way of recovering.
^L to refresh does not work, nor can you run any other commands such as save (^O) or even exit (^X).
The only way to recover pico is to resize the Terminal window to exactly what it was set to before the resize -- hopefully this was your default Terminal window size. pico then magically reappears, with all its functionality restored, and your text in place!
[robg adds: When I tested this, I found that as long as you made the window no larger than your previous window, then all the text would reappear. So you can just resize down to a notably smaller size, and you'll get everything back. But if the new size is even one row or column larger than the original, you'll still have a blank screen. Quite odd.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060111042528978