Salesforce.com and VMware announced a significant joint service called VMforce that allows developers to run Java applications inside Salesforce’s cloud. I would encourage you to read Salesforce’s blog announcement on this as it is quite detailed with regard to what it is and more importantly, why it matters.
From where I sit this seems pretty significant even if Java has strong competition from other development environments for hosted applications. What it means is two things, enterprise Java apps now have a clear path to the cloud, and secondly Java developers have the ability to write apps that take advantage of well established database, identity management, integrated search and mobile capabilities without having to adopt new frameworks or toolsets.
Time will tell whether or not Salesforce is successful in wooing Java developers but I have no reason to believe that they will not be. This partnership takes advantage of widely adopted services like Tomcat, Eclipse, and the Spring Framework, which reinforces the core messages that Java developers are welcome up in the cloud.
Several Enterprise Irregulars have offered their views, I would encourage you to read them: