I accidently deleted a post due to getting confused with the "delete post" UI. I've posted my thoughts (with screenshots) at http://engtech.wordpress.com/2006/06/14/wp-bug-with-deleting-posts/
I would actually go as far as saying this is a "WP bug", although it really boils down to confusing dialog.
The summary (for those who didn't click on the link) is that when accidently hit 'delete post' followed by CANCEL it then gives you a second ambiguous "do you want to do that? y/n" dialog where "Yes" means you want to delete the post and "No" means you want to save the post, which is counter what you would expect having just hit cancel.
I think there is a problem in general with the "Are you sure you want to do this?" dialog because it never, ever mentions what you should be sure about and the same dialog is used whenever you edit posts as well.
(I would even go so far as to say that the Delete Post button is placed where a Submit button should be, but at some point you have to suck it up and admit your mistakes :) )
I love WP and I think it's the best thing out there, fixing minor issues like this will only make it better.
And if there's anything that can be done about recovering that post (I've sent WP feedback and contacted atomattic), it would be greatly appreciated.
Also, some kind of recycle bin for deleted posts (similiar to the mechanism for drafts, I imagine) would be icing on the cake.