This just started today (9/26/2011) and won't let me save the file to force.com. The file is a long existing apex class. Only making some minor changes.

Save error: Unable to perform save on all files:

com.salesforce.ide.api.metadata.types.Metadata$JaxbAccessorF_fullName cannot be cast to com.sun.xml.internal.bind.v2.runtime.reflect.Accessor

I deleted the whole project and re-added it. I was able to get everything back, then tried to make changes again. Same error. I tried to refresh my file from the ORG and received a pop up with the same error.