Here is a neat tutorial showing how to create an urban design by layering different types of vector elements. In this tutorial, you first create a range of concentric circle stamps (or “brushes”), and layer them on top of different coloured cloud silhouettes. Finally, you create a whole bunch of swirls using the spiro curve and path effects.
Here is a comprehensive video tutorial, (created by syllie) that demonstrates how to use the awesome new spiro swirls feature in Inkscape 0.47, which was released in November 2009.
Updated this tutorial to link to the archive.org version. (the original does not seem to be hosted any more)
Here is another awesome tutorial from Andy Fitz. In this tutorial, Andy experiments with the new spiros Live path effect, combining it with the existing and equally awesome patten on path LPE. The link to the tutorial is after the break.