Are subdomains no longer separate sites in the eyes of Google?

When did subdomains start appearing in a Google site: search? In other words, a site:www.somedomain.com used to only show results with urls from www.somedomain.com.

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Google has not solved the subdomain issue

Although Google has manually nuked the billions of pages that Mr. Spammer got indexed, it has obviously not solved the problem algorithmically. Would you consider Craigslist to be a spammer? No, of course you wouldn’t. Yet the rankings show some very obvious problems that Google is having with subdomains (sub subdomains actually) by looking at certain search terms (here and here). For those two terms, Craigslist (using sub subdomains) gets 97 of the top 100 search results and 50 of the top 100 results.

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For SEO: Subdomains, Folders, or Separate Domains?

SEW has a great thread going that clarifies when it is best to use a folder structure, a subdomain structure, or a different domain structure. This question comes up a lot, and the answers given in the thread are top-notch. Ian clearly explains when it is best to use which type of structure, depending upon your linking strategy and goals.