Backtype have patched the python scripts to support spot instances (http://tech.backtype.com/patching-the-cloudera-ec2-boot-scripts-for-sp). It would be good to incorporate this change.
note java support is via jclouds and this feature is pending the following, scheduled for beta-10 release
here's a patch to ad spot instances to the python scripts in whirr 0.3.0
here it is.
I believe we should commit this change even if you are not going to work on the python scrips.
I've just committed this.