Debug Bar is great plugin, but it has one big problem - it doesn't display errors, that appeared after Admin Bar (and Debug Bar accordingly) render.
So after Admin Bar is rendered - Debug Bar begins to render:
debug-bar.php, line 34 add_action( 'wp_after_admin_bar_render', array( &$this, 'render' ) );
And so after that the main content part begins to render (in my case - plugin's options page). If errors will occur during render - they won't be logged, because Debug Bar is already rendered.
What I propose?
Debug button and Debug Bar contents part separately. We render Debug Button in Admin Bar, and contents block in footer. Using JS we can just show this blog on button click.
Using this way we can log most of errors, not only errors before Admin Bar render.