What is the text box on the desktop for?

If I click on the desktop/background picture in Ubuntu 11.10 (Unity) and start typing text, a little text input box appears containing my written text. If hit return the box goes away along with the text.

What is this for? I am just curious. Is this a lovely feature I am not enjoying the functionality of due to my ignorance?

That is the GNOME3 desktop Nautilus search integration.

You can test that by giving the desktop focus and start typing something that exists in your Desktop, it will jump to that item.

The textbox that appear on the lower-right corner of folder windows including the desktop itself (as well as in a variety of other applications) lets you type in text that is matched to the beginning of each item present.

For the desktop, files and folders are automatically selected if their names start with the characters you type into that text box. This feature allows you to select an item on the desktop, in another folder, and in many other applications (for example, some music players) by typing in the first few letters in its name.

This text box comes up when you start typing; if you want to dismiss it, press Escape (or click elsewhere, including the desktop itself).

You can't write on to the desktop itself (not even in Windows). The window you see is a kind of filtering of files etc as said in those answers.

Use widget named sticky notes to easily write note on desktop. Or you can create an expux document and open it to write txts.