1. Clustering Support
As I can collect from "Oracle + Sun: Application Server webcasts" and other resources, Glassfish v3 will probably never have centralized clustering feature available.
You can use mod_jk today with GlassFish v3 (but no centralized admin/nodeagent yet & probably never).
The slide #15 of the Oracle + Sun: Application Server webcast states:
Glassfish will be for productive and agile development.
Weblogic is the availabillity and scalability solution.
Therefore the v2 was the last GF with clustering facilities.
The centralized clustering feature was supported in v2 and therefore Glassfish v2 was the last Glassfish with clustering facilities.
2. Future Licensing terms may change for some GlassFish modules
Most of the components of the GlassFish plattform are available under a
Dual License consisting of the Common Development and Distribution License (CDDL) v1.0 and GNU Public License (GPL) v2. Details for GFv2 can be found on the Glassfish Wiki. This will stay the same for most of the modules. Except for the modules which will be part of Weblogic 11g, and most probably those 3 are
(Metro, Jersey, Grizzly)
3. There will be tool support for migrating Glassfish Apps to Weblogic Server
The complete development to production staging process will be addressed by upcoming Oracle solutions.
JDeveloper and/or OEPE will have plugins/support for automatic migration of Glassfish apps to Weblogic.
The Weblogic split deployment directory structure will also be enhanced with staging features.
There will probably also be new maven plugins supporting dev and productive builds with Glassfish and Weblogic.
4. Two camps may be emerging with these steps from Sun+Oracle
One camp will be for the already established big fortune 100, 500, and 1000 companies who will go with the big solution, fully integrated, and costly technology provided by Sun+Oracle,
while another group of technology savvy/capable organizations (e.g. Google, and Yahoo), going the way of stringing together best of breed open source solutions already out there. These solutions may be run on a grid of hundreds/thousands of commodity hardware or on some cloud platform.
In fact, now I can see more areas/avenues need to be addressed by open source community. So fellow developers, I think its time to start contributing more to open source.
BTW, Despite so many feature support on Glassfish v2 and other app servers, "Tomcat" is still my first love and will remain forever :). Thanks to Jakarta & Apache Open source developers.
Some resources to read more on my source of thought:
Oracle + Sun Product Strategy Webcast Series
GlassFish vs. WebLogic - 10 visions for the future
Oracle for big businesses, open source for other businesses?
GlassFish v2 Wiki
Glassfish v3 Node Agent Question in java forum