There is a small problem with latest version of Android SDK tools revision 17. It will not bother you if your project doesn't use any JAR dependencies. As reported in our JIRA the output of our build misses classes from JAR libraries that are contained in libs folder of your project. Note the content of JAR referenced by library projects is included correctly.
I initiated some discussion on ADT-dev mailing list to see if there is a chance to fix this problem and will look for some solution. Meanwhile there is a workaround to set the working directory for your IDE to your project directory (simply start it from this directory). Or more complex one can be to create an Android Library project and move these JAR there.