The Bounceback History Statistics report shows you, at a high level, what types of errors you are seeing from your email marketing efforts, in order to identify high level trends. If you are seeing high levels of spam notifications, or unknown users, you will need to look into your lists or practices to better understand how you can improve your deliverability rates.
Deliverability is something to continuously watch, manage, and improve. I wrote a bit about the general topic here http://digitalbodylanguage.blogspot.com/2009/02/all-you-never-cared-to-know-about.html on the Digital Body Language blog to give you a sense of the overall approaches. Now with deeper bounceback reporting within Eloqua, you can better manage and monitor your own deliverability success.