I'm posting the solution Ive found to successfully removing the p tags from the TinyMCE editor considering the grief it has given me, it might be useful to someone else.

I understand there are people who believe the p tags are necessary, but I much prefer <br /> tags and think they provide much for cleaner code.

There's also a css 'solution'.

p{
margin:0px;
padding:0px;
}

But my preferred solution below.

CustomLeftAndMainDecorator.php

<?php
class CustomLeftAndMainDecorator extends LeftAndMainDecorator{
   function init(){
		$htmlEditorConfig = HtmlEditorConfig::get('cms');
		$htmlEditorConfig->setOption('forced_root_block','');
		$htmlEditorConfig->setOption('force_br_newlines',true);
		$htmlEditorConfig->setOption('force_p_newlines',false);
		$htmlEditorConfig->setOption('convert_newlines_to_brs',false);
		$htmlEditorConfig->setOption('invalid_elements','p');	
		$htmlEditorConfig->setOption('paste_auto_cleanup_on_past',true);
		$htmlEditorConfig->setOption('paste_remove_styles',true);
		$htmlEditorConfig->setOption('paste_remove_styles_if_webkit',true);
		$htmlEditorConfig->setOption('paste_strip_class_attributes',true);
		}
	}

Add to mysite/_config.php

Object::add_extension("LeftAndMain", "CustomLeftAndMainDecorator");

On windows you can do <shift><enter> to create a <br /> instead of a new <p>. giving you the best of both worlds. Works on mac too I think