Can I delete the Year and Month Image Folders?

http://websiteURL/wp-content/uploads/2011/05/logo.png

On the server in the folder “wp-content/uploads” it seems images are being stored by year and month. Is this the default and is there anything wrong with deleting the “2011/05” portion and just have my images upload to:

http://websiteURL/wp-content/uploads/logo.png

or will this really mess up the images I have already uploaded?

Thanks