My personal experience so far is good; I have upgraded all 3 of my slices and have not yet seen any issues. However, I can't guarantee that you will experience the same! Be sure to read the release notes to see what's changed before charging gung-ho into an upgrade!

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Java Test Class
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import java.sql.Timestamp;
import java.util.Calendar;
import java.util.TimeZone;

public class Test{

        public static void main(String [ ] args){
 TimeZone tz = Calendar.getInstance().getTimeZone();
 System.out.println(tz.getDisplayName());
 System.out.println(tz.getID());
                System.out.println(System.currentTimeMillis());
                System.out.println(new Timestamp(System.currentTimeMillis()));
        }
}