If you are interested in helping out with the development, or just want to look through the source code (it is released under the GNU General Public License), it can be checked out of the repository using Bazaar with this URL: http://www.kallisti.net.nz/bzr/emusicj/trunk, or you can browse it. Bug reports and feature plans can be seen and added to. If you want to help out, get in touch. For more information about things, have a look around the Trac site. This is where any information relevant to developers lives.
If you have a feature you'd like to see in it, you're welcome to let me know by adding it to the system or emailing me, or (even better!) implement it yourself and send me a patch. If you'd like to do a bit more work than just that, I can provide commit access to the repository.
If you feel like getting your feet wet with the code, or just helping out for the good of the eMusic-subscribing community, check out the Roadmap of features and changes that need to be done.