Benjamin Klein sent me a quick email about the release of The VimL Primer: Edit Like a Pro with Vim Plugins and Scripts. It's a short book that will be published on The Pragmatic Bookshelf.
It will be around 100 pages, and is meant to be released in January. It sounds ideal for those of you who want to get started scripting your own Vim plugins:
The VimL Primer ... gets you comfortable in VimL quickly, walking you through creating a working plugin that you can run yourself as you write it in Vim. You'll learn how to script common commands and buffer interaction, work with windows and buffers from within a plugin script, and how to use autocommands to have Vim recognize entirely new filetypes. You'll discover how to declare filetype-specific settings and define your own syntax elements for use with Vim's syntax highlighting. And you'll see how you can write your own command-line commands and define new mappings to call them.
Benjamin has previously written for GroovyMag and has contributed to Grails 2: A Quick-Start Guide.