The preview release offers you to stay up to date with the latest gGo development. The previews are testing and development versions. You can help me a lot if you test the newest features and post bugreports to the gGo mailing list or email me directly.
A word of warning: The preview release is not considered to be stable. Usually it should work, but I can not guarantee it. This is a testing release, not the latest stable version. Only use this if you are willing to do some testing.
Please note the previews are only available on the gGo webpage at http://panda-igs.joyjoy.net/java/gGo/ and not on the mirror at http://www.pandanet.co.jp/java/gGo/.