I've found out MarsEdit today and well I was just like... waaah that's what I needed! I really love it!
Thus I've no bug report or anything. My remark targets ergonomics.
When I want to send a post to the blog, a pannel appears saying "Posting edited message to...." with a circular progress indicator. The point is it takes about 15 seconds to send my post, and during that time, I feel like I must wait and do nothing else (yeah I know I can go on using MarsEdit and let that window alone, but that's not my first thought). Thus I stay in front of my screen.. waiting.. and that's an annoying feeling.
Then the window disappears and I can see the Growl notification.
So, the perfect solution to me would be to be able to get the following behavior :
once I click the "Send to Blog" icon, the window is immediately closed and "something" shows that the post is being sent. Then, as usual, the Growl notification appears. Cyberduck's behavior looks like a good example.
The "something" could be an informative text in the status bar of the main window or the same informative text in a column of the table where you have all of your posts listed. You could have an icon representing something like "posting", "posted", "failed".
Now what about if the sending fails ? I'd suggest reopening the post editing window with a panel telling what's wrong.
Conclusion : I'm trying to help you improve MarsEdit as I really like it. And I know it's not my job to give you possible solutions, I wrote them especially in order to show I'm not asking an impossible-to-do behavior. And well.. ok, as a software development student, I enjoy thinking of the possible solutions :) .
PS: English is not my mother tongue so I hope there won't be any misunderstanding in the phrases I used :| .