Do you know how to use it?
The KML support is tied into the XML facilities for encoding and parsing geometry.
The GeoTools user guide has replaced the wiki links provided by Ian above - with a nice clear page devoted to wrangling geometry and XML:
One of the headings on that page is devoted to KML.
Site policy here asks that we include the answer rather than just provide links. With that in mind:
Or to parse KML you need to consider geometry and style as KML includes both. Here is an example that fetches a collection of features back.
You can also ask it for a stream of results (incase the file is bigger than memory):
Best of luck (and if in doubt review the test cases).
There is a KMLExample at http://svn.osgeo.org/geotools/trunk/demo/example/src/main/java/org/geotools/demo/xml/KMLExample.java which shows the KML bindings in use for writing. From other discussions on the user list it seems that the KML bindings work in a similar way to the GML bindings so look at http://docs.codehaus.org/display/GEOTDOC/GML+XML+Support for more clues.
When you get a solution feel free to post it to the GeoTools wiki.