Question: I'm just wondering if display:none is affecting my sites seo as I have for certain keywords dropped rank in google over the past few days since implementing this into a new homepage re-design.

I am using wordpress and displaying random post images on the homepage, getting the excerpt and hiding it using display:none and when a user hovers the image it displays the excerpt as a tooltip. 

I have read a few conflicting articles on this and watched Matt Cutts youtube video but that doesnt really give me an answer for the way I have implemented it. 

So I am hoping someone on here can give me a bit more insight as to whether it is not good seo practice or doesn't make much difference?

Thanks

Answer: 
Although you apply `display:none` style to your element, it doesn't matter with seo because your element dom still exist and what seo looks for is the dom and its content, not UI.
I don't claim to be an SEO expert, but generally speaking if you're trying to fool the site crawlers (by hiding tons of keywords) that's bad for SEO because you're likely to get blacklisted. If you hide content because it helps user interface, shouldn't be any negative effects. Since it's an automated process, err on the side of caution generally because, for example, if you're blacklisted you can't argue your case for including every city name in the lower half of the state in a hidden div.

Crawlers are apparently not very good with JavaScript (and many users have JS disabled anyways) so perhaps have the content shown by default then hide it with JS/CSS hover.