You can fix the JDK today
We have been accepting code contributions, for bug fixes, from the public for over a year. The program is described on the mustang.dev.java.net project page. Essentially the idea is, if there's a bug you see that you want fixed, rather than wait for a Sun engineer to make the fix that you do it yourself.
At Java ONE three of the contributors were interviewed and a recording of that interview has been posted. The interview is very nice, and should give you a good introduction to the process, from the people who are participating.
The process requires you sign a "Sun Contributor Agreement", after which you will be given a jdk.contributor role on the Mustang or Dolphin projects. After that you find bugs you want to fix, make the fix, test it, and then send it to us. After you do that, we will work with you to get it integrated to the JDK source.