I stumbled onto the Shape » Draw With Pen menu option in Pages, and soon discovered text would wrap around the curvy lines I had drawn. You can use the lines to shape the margins into wavy columns of text, or to add creative slashes through the paragraph.
But, how can you do it without the lines showing up? Simple: select the line, then use the Graphic tab in the Inspector panel to make the line white. Ah, but then you can't select the line to manipulate it or delete it. Solution: slowly move the cursor over the space where the line sits. When it changes from an insertion beam to an arrow, click to select the invisible line. Click once more and it will show you the break points. Click a break point to modify the curve.
[robg adds: Instead of making the line white, another option (assuming you're fine with a one-pixel wide line) is to set the Stroke to None in the Graphic tab of the Inspector. Then, when you click on the box holding the line to select it, a gray line will appear, showing the path of the line. You won't see this path if you set the line color to white.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090802163025633