FULL PRODUCT VERSION :
jdk 1.4.2
jdk 1.5.10
jdk 1.6.2

ADDITIONAL OS VERSION INFORMATION :
I have tested this on:
windows xp
windows vista
mac osx
mac g4
ubuntu 3

A DESCRIPTION OF THE PROBLEM :
the decimal and thousands separator are reversed from what they are supposed to be.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
create new Locale("es", "US") and then format any number.
compare to new Locale("es_US") and new Locale("en_US") as well as new Locale("es_ES") or new Locale("es_MX")

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
2,000.00

ACTUAL -
2.000,00

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package com.java.test;

import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

public class LangTest {
    private static final List<Locale> lst = new ArrayList<Locale>();

    static {
        lst.add(new Locale("es", "US"));
        lst.add(new Locale("es_US"));
        lst.add(new Locale("en", "US"));
        lst.add(new Locale("en_US"));
        lst.add(new Locale("es", "ES"));
        lst.add(new Locale("es_ES"));
        lst.add(new Locale("es"));
        lst.add(new Locale("en"));
    }

    public static void main(String[] args) {
        for (Locale locale :lst) {
            processLocale(locale);
        }
    }

    private static void processLocale(Locale locale) {
        NumberFormat nf = NumberFormat.getInstance(locale);

        System.out.println(locale + " " + nf.format(29.99));
    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
new Locale("es_US")