The QuickLogin plugin for self-hosted WordPress sites adds Squarespace-inspired detection of Escape key to login to the site. Just install the plugin, and pressing the "Escape" key while viewing your site will present the login panel if you're not already logged in, returning you to the page you were viewing after login.

If you are already logged in, pressing the escape key serves as a convenient shortcut to access the wp-admin interface for your blog.

To install this plugin, just copy the "QuickLogin" folder to

[YourWordPressSite]/wp-content/plugins/

And then enable the plugin from your WordPress admin panel plugins page.