The biggest deterrent of this book is the fact that the premise of online usage is now dated. Written in 2002, before the era of Facebook and Twitter, O'Conner and Kellerman focus primarily on e-mail and obsolete online chatrooms. Despite that, many of their "getting it right when you write online" tips made me laugh, and my copy is now dog-eared for future quotability.
As always, O'Conner's take on grammar and punctuation kept me in a perpetual state of laughter and/or cheering the grammar underdog. Their rules for writing online can easily be applied to newer sites, including Goodreads, so I would still recommend this as helpful and humorous reading material.