Every day, the team over at Google's headquarters makes advances in Search Engine technology. A few years ago they announced the ability to read Flash websites, and then last year they further announced the ability to read deeper inside Flash websites.
Unfortunately, Flash websites still suffer from lower ranking than normal HTML websites.
In 2010, Google admitted that they have trouble reading websites that rely on JavaScript or AJAX. The Googlebot spider is not able to provide the user input needed to display website information that to us would be very simple to interact with.
The result is that websites with heavy JavaScript and AJAX programming are penalized similar to Flash websites. A simple home page rotating image is nothing to worry about, but you should worry if all the menus on your website rely on Java...
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