Hidden Text CSS is now readable by Googlebot? Well, here is some discussion on DigitalPoint forum on this topics:-

how can google automatically confirm that css is actually being used to hide text. Surely a human would need to confirm. For example, if I wanted to hide text i might use css to make my text the same colour as the background which Google could maybe check automatically but what if I use css to make my text the same colour as a background image? I say this because google obviously….

Personally I think Google will sooner or later fix up all the tricks, including trick like hidden text css.

Source