Based on a post here in the forums, I did a little testing and it now appears like wordpress.COM allows multiple spaces between words and sentences. Those wanting two spaces between sentences no longer have to jump through HTML hoops to get them. Just press the space bar multiple times and the spaces will be kept in the editor, and in the published post.
You can now also have multiple blank lines between paragraphs as well. Just hit the enter/return however many times you want. Again, no more HTML tricks are required.