So if you have the following code:
< div id='test_1' class='field_1 field_2' >.inner_text
Then you can only select @document.css(".field_1").inner_text in version 0.3.9. However, in version 0.4 I assume I should be able to do something like @document.css(".field_1, .field_2").inner_text.
The other bug fix that might make the test more stable is the fix for some obscure selenium bugs by changing the default from localhost to 127.0.0.1.
To see the complete changes to version 0.4.0.rc, please visit Capybara site.