Google just announced that their AppEngine will support Java. The good new: AppEngine is going to use a fairly regular JVM, with some functionality disabled like sockets and file writing. It should support other languages that compile to bytecode, like Scala or JRuby. ~~No mention of Groovy, but i hope that’ll work soon too~~. Update: Groovy is supported on Google App Engine. Unfortunatelly, no socket support will probably mean no ESB in the cloud. Would be nice to run Apache Camel or something similar on AppEngine.
Some interesting information about running java on GAE: