title: Pandas 'describe' is not returning summary of all columns
body: <p>I am running 'describe()' on a dataframe and getting summaries of only int columns (pandas 14.0). </p>
  
  <p>The documentation says that for object columns frequency of most common value, and additional statistics would be returned. What could be wrong? (no error message is returned by the way)</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>I think it's how the function is set to behave on mixed column types in a dataframe. Although the documentation fails to mention it.</p>
  
  <p><strong>Example code:</strong></p>
  
  <pre><code>df_test = pd.DataFrame({'$a':[1,2], '$b': [10,20]})
  df_test.dtypes
  df_test.describe()
  df_test['$a'] = df_test['$a'].astype(str)
  df_test.describe()
  df_test['$a'].describe()
  df_test['$b'].describe()
  </code></pre>
  
  <p><strong>My ugly work around in the meanwhile:</strong></p>
  
  <pre><code>def my_df_describe(df):
      objects = []
      numerics = []
      for c in df:
          if (df[c].dtype == object):
              objects.append(c)
          else:
              numerics.append(c)
  
      return df[numerics].describe(), df[objects].describe()
  </code></pre>