WKB4J-1.0-RC1 has been tested to work with the last release of PostGIS (0.8) and the last release of PostgreSQL (7.4). Hopefully, PostGIS does not have to be patched anymore to work with WKB4J.
WKB4J reaches 1.0 RC1. The only problem holding back the final release is that WKB4J has not been tested on enough computers. Please go ahead and give it a try.
There is virtually no difference between 0.8 and 1.0 RC1.
Don't trust the activity or cvs statistics, they have been broken for a few months. It seems that Sourceforge.net is working on the problem: http://sourceforge.net/docman/display_doc.php?docid=17790&group_id=1#statistics
Today, a much newer version of WKB4J was released. It has complete support for all OGC's geometry types (but GeometryCollection). It is compatible with OpenMap, JTS and Postgis. All the functional tests pass and the performance test are very good. It is still be beta because there is a still a few things on the "must-have" list. Check the news page on the website: http://wkb4j.sourceforge.net/newshistory.html
Today WKB4J released its first distribution through the SourceForge.net system. Theses files were previously distributed through the project's website, so they are only interesting for historic reasons. The first usuable release is expected very soon.