Update (10/10/14) – I recently found this video that talks about how hidden text is a no-no in SEO for obvious reasons, the primary one being that you can hide keywords this way. Matt Cutts, head of Google’s web spam team, talks about why this violates Google’s quality guidelines in the video below. The important thing here is that Google is stating they’re reading these sorts of things, so yes, Google does crawl CSS display none content.
A sure fire way to test this is to do a site search using the URL that you have ‘display:none’ in your code and hide some text in the code using a goofy made up word. Then do the site search and include that word. Use Webmaster Tools and fetch as Google to get immediate results.
Regarding CSS’ display:none, hiding something from Google is only bad if you’re intentionally trying to manipulate search rankings.
Hidden options and text from visitors is now a common practice given how interactive websites have become, so you shouldn’t worry. In the past, people used these sort of methods to game the SEO, hiding keywords and links etc. The result it that when Google crawls a site that has things hidden from the viewer, it views that site as less trustworthy.
You can see exactly how Google is reading your web pages by submitting a sitemap to webmaster tools. Some helpful links below.
Does Google Crawl CSS ‘display:none’ Content?: Your Response
If you’ve tackled this question in the past or run into any interesting case studies, drop me, Cort Tafoya, an email at firstname.lastname@example.org. Due to the algorithm updates Google has made and their effort to fight spam, we know they’ve found ways to read people’s display none and hidden div content. It’s too easy to cheat at SEO by using these CSS tricks, so Google has updated its crawling capability accordingly.