The region editor seems to have a really small text area size. Adjusting it is pretty deeply hidden so I wanted to share:
The modal window that pops up when you click the Edit region link is controlled by the CssClass name. The default is "submodal-640-480". Change the "640" and/or "480" to something new will change the size of the modal popup window.
The text area is controlled by the edithtml.ascx control found in admin/controls/content/html/edithtml.ascx. Line 5 has a "height" attribute that will change the height of the text area.