One way you can really help the GeoServer project grow is including a 'powered by GeoServer' logo on your mapping application. To do this just add the following html to the appropriate spot on your page:
<a href="http://geoserver.org" ><img src="http://sigma.openplans.org/images/geos-90x33.jpg" width="90" height="33" border="0" alt="GeoServer Logo" /></a>

You can see an example of this at http://sigma.openplans.org