I'll mention this first before getting into the CSS, which is a little tricky.
For your posts to show up in the global tags pages here, and to keep from getting on the bad side of the search engines, you should limit the sum total of tags + categories on a post to no more than 12. Anything more than that and you risk getting left off the wordpress.com global tags pages and the search engines can also get suspicious and might discount your search engine ranking.
The author can be moved up beside the date, but the issue is the length of the "month name. Since it can vary considerably (May vs, September as an example) the author would have to be spaced over to the right far enough to handle something like September 30, 2011. That means that on a date like May 1, 2011, there is going to be a large gap between the date and the author.
It might be better to put the comment link below the beside the author where it is and then move the tags down beneath them.
One thing to consider though is that most people will read a post and then decided to comment, and with the comment link at the top, they have to scroll back up to the top of the post to get to the comment link. Just something to contemplate.