Blogger, Adsense, and Google's mail servers weren't enough. Now spammers have moved on and hit Google Docs as well. MessageLabs senior anti-spam technologist explains:

What's happening with Google Docs is that Google Docs is a way to publish your documents online. So, for example, word processing documents and spreadsheets and so on, and much like if you were using Microsoft Word you can embed links within those documents. What this does for the spammers is it allows them to effectively publish online a Web page on hosting sites such as Google that has all the bandwidth in the world for hosting it, and it's also a Web site that is never going to get blacklisted by anyone because nobody would be stupid enough to blacklist Google. So in effect, for the spammers this is a human shield effect. They can host their information and links online on a very stable source of bandwidth and links, and not worry ever about it being taken down or blacklisted.

There is a great podcast on CNET with more info. Check it out here!