No Documentation on how to use Java.
Googling for AppFog Java gave back broken 404 links to github.
Googling for AppFog Java gave back broken 404 links to github.
Heroku Java deployment is "unusual" and there are many Java developers out there that prefer WAR/EAR that complies with JEE5 (legacy purpose) or JEE6. If you can achieve that, get ready for massive users, I know there are people who don't like GAE model for various reasons.
Basically: make it like Jelastic and don't limit it like CloudFoundry (no EJB 3.1, etc etc).
JavaEE deployment model is preferable over some "weird" setups.
The only Java-friendly PaaS so far is Jelastic simply because they support GlassFish and Tomcat utilizing standard deployment model. But Jelastic does not provide the infrastructure (data-center or AWS, whichever), they partner with hosting providers, which I think is not a great move.
If AppFog can come up with a more standard/sane Java PaaS model out there, you guys can win that particular market.
If I may suggest more:
1) Tomcat 7 instead of the older 5 or 6.
The JavaEE landscape has changed significantly from J2EE 4 to JEE 5 to JEE 6 in which each major version moves toward _way_ less code and reduce XML/settings/configurations to a very minimum.
2) TomEE (if possible, or as "add-on"/next-level offerings)
Tomcat 7 implements a subset of JavaEE 6 (known as the "web-profile": Servlet[controller], JSP[template], JSF[view/controller], Dependency Injection, JPA[orm])
Enterprises who are still in love with EJB 3.x need TomEE.
3) Maven for deployment (feature/option)
Use Maven for deployment.
Try openshift.com, has full Java EE server with both free and supported options.