I personally believe a complete customization option for the login page to match the rest of main site would be a great improvement to the current 'Login Image' and the 'Custom Login CMS' options in the Ultimate Branding plugin.
It's great that I can change the WordPress logo on the login page, but I only have a very basic understanding of CSS and would have no idea how to change the colours/fonts on the login page to match the rest of my site using CSS.
The s2Member plugin has a complete 'fill in what you want to change' section for designing/customising the login/register pages.
I've also noticed Ultimate Branding asks for logos to be "310px wide and 70px tall", whilst the wp codex states "logos should be no bigger than 323 pixels wide by 67 pixels high".
The 13 pixel difference in the width is possibly why my logo is just off center above the form on my login page.
For reference, s2Member can be installed from plugin repository. The 'Login/Registration Design' option is halfway down the 'General Options' page.
You'll see it's very comprensive.
May I suggest this feature to improve your already very useful Ultimate Branding plugin?