Ever use Google to search for information, and click on a link provided only to find the site isn't coming up? Then, returning to Google and clicking on the "cache" link to the site? I have, and it's vey useful.
But, is it ok for Google to have copies of web sites like that? I'm not sure that I want to make the argument for or against. It has helped me in the past.
But, there is a concern being voiced by some people on the web. There's an argument that I've seen a number of people make in web forums. It was only a matter of time before mainstream media took a closer look at Google's cache. Especially since it can provide looks at pages they've archived, to be retrieved for a price.