What you did is proofing that google indexes hidden text. What you did not proof is how that impacts your ranking. Google will know that this text is hidden, although it is indexed and that is what is important.
Exactly. I see many comments here about hidden text, switching user agent, css and bunch of things that don't work anymore. The reason why we used to use that stuff was because Google used to read the whole page and use Keyword Density as one of the many ranking factors. Since those factors aren't used anymore and you can also get penalized, there's no reason to do it. Unless you want a page with just one picture and no text, but still get the benefit of the content, there's no reason to do it.
I suspect there will always be a way to hide the text in a way that a search engine won't be able to detect. You can do this without applying any properties directly to the element containing text (raise other elements above it), hide it with JavaScript, or any number of such techniques.
I believe Google is moving towards graphical understanding of the text as well and it should be able to render the pages and see what is going on the page... those days will soon be over and technical excellency in SEO will talk.
I think its known Google can masquerade as a "normal" visitor if it suspects you of cloaking (non identifying UA string and coming from a non disclosed google crawl IP)
