It is basic search engine optimization (SEO) knowledge that you should tag every blog article that you will make with keywords you want to top in order to increase the chances of successful results.However, it can end up in disastrous results if you do not know how to plan carefully. Here's a comprehensive report about LibraryThing.com and Amazon.com and the way they used tagging. Apparently, according to LibraryThing.com, Amazon failed.
Link: Thingology (LibraryThing's ideas blog): When tags work and when they don't: Amazon and LibraryThing