There is often much talk about different types of search engine optimization referred to by a hat color. For those out of the loop, white is good, and black is bad. Or to put it a better way, white is rule abiding, and black is anything goes. In this article I will more fully define what it means to be wearing one of these hats, as well as discuss some of the pitfalls of one hat over another.
White hat SEO is more and more becoming almost nothing. To sum it up succinctly I would simply say that white SEO is the optimizing of a website for people first, almost pretending that search engines did not exist. With white hat SEO your primary goal is to make a good quality site, and then to let the rankings come naturally as a result of your quality.
If you're doing just white hat SEO you'll optimize your site to be accessible, using ALT & TITLE attributes in your anchor and image tags. You will make sure your menu is simple descriptive text. You will produce good unique content first, and focus only second on placing keywords within that content. Almost every optimization you make will be as much for your users as for search engines. The exceptions will be technical optimizations you make to ensure your site is easy to crawl, such as removing Session IDs from the URL, using Search Engine Friendly URLs, or the like.
In your off-page optimization, specifically the building of incoming links, you will work only modestly at it and you will not engage in link exchanges or any other artificial linking for the purposes of increasing your rank. Mostly you will try to obtain links naturally by building good content that people want to link to.
Gray hat SEO is changing in that some things that were once white, are now gray. Gray hat SEO includes things like publishing duplicate content. Multiple, otherwise white hat, sites that have the same content. Gray hat SEO also includes mild artificial linking schemes.
So if you were doing gray hat SEO you would perhaps use a tool like the Digital Point Coop Ad Network. You would probably more aggressively include keywords within your site's content. You would certainly also do all the optimizations a white hat SEO would do, but you might take them a little further. For instance you might overly use image ALT tags to put in more keywords, even when it is unrelated to the specific image. With gray hat SEO you aren't afraid of link exchanges and may even do an off-topic link exchange (dark gray to be sure) if you think it'll raise your PageRank.
Mostly, gray hat SEO includes things that may be frowned upon, or could even result in a penalty, but they are very commonly done and they aren't forbidden as strongly as black hat acts. For instance gray hat linking schemes may get your links devalued, whereas black hat linking schemes could get your site banned.
Black hat is doing everything that the search engines say you shouldn't. Black hat techniques includes cloaking, automated link spamming (forum/blog spamming) robots, anything hidden (including links or text), deceptive redirections, stealing copyrighted content and publishing it (ala scraper sites), multiple (thousands) of sites with duplicate content all interlinked with hidden links and cloaked.
There is no right or wrong hat. Some people take a moral viewpoint and feel that white hat is the only way to go. Others think that black hat is the way to sure success.
My own personal experience has formed my belief that fundamental white hat SEO is the way to go. In truth I guess I am "off-white" in that I do sometimes use somewhat artificial linking schemes, but only very minor ones.
I have done gray hat sites before, but I've made the same observations I read about today in Andrew's Blog, namely that the sites I've had that were white hat are successful, the gray hat sites (usually sites with generic non-unique content, or sites with artificial linking schemes) are not. So the basis of me choosing white over gray is simple economics. In the long run, white hat sites are the most profitable. They go on earning forever, whereas black hat sites only last until they are banned, and gray hat sites typically fall when search engines release a new algorithm that is better at finding the little gray tricks. It is the tortoise and the hare. Additionally, typically spamming black hat sites never get bought out by larger companies, whereas good quality content sites do. So if a big buyout is your ultimate goal, keep things up the up and up.
If you read that blog post linked above you'll also find it touches on something I wrote awhile ago, namely my article on planning for longevity. Basically if you want to experiment with these darker techniques that is okay, just keep it segregated from your other sites and realize too that these may just be short term earners for you and it is important to have long term, reliable, proper sites as well.
As for why I do not do black hat. Most, but not all, black hat has to do with either spam, or copyright infringement, neither of which I'm a fan of. Both annoy me on a daily basis, and I decided that I will not be part of the problem. If however you wish to journey to the darkside, this blog is a good starting point.