Thanks to Bruce Schneier for linking to this interesting article on using patterns in language to identify the author of emails. While the technique would not allow them to identify your anonymous emails in an ocean of others, that is rarely the real world threat scenario.
In many cases there is a relative hand full of likely authors of a given email or group of emails. It is often possible to gather large samples of emails known and acknowledged to be from the likely authors. In that case this technique has a small group of targets and excellent training materials which allow for very high levels of accuracy (the authors of the paper claim 80% - 90%). That is probably enough to get a warrant to search your home and computers.
Unless you have been unusually careful, the gig is probably up by then. Remember, this might not be for criminal matters. It many cases this would come up in whistle blowing or other non-criminal situations.