Just to add a counterpoint to this discussion. And this comes from the seo forums and filtered through me, so it may not be exactly on, but…
If you have a site that you add content to on a regular basis, say a few pages per week, google will love you. You will end up with a very large site by the time you get out of the sandbox, and every page on your site should be considered a gateway into your affiliate codes. Take a look at your traffic stats, not everyone lands on the home page.
You can just as well target keywords on a page by page basis as you can for a full site. When you are trading links, you simply have the site you are trading with link to the sub-page instead of your home page.
Also, by having a large site you can micro target keywords that very few sites are competing for as long as your on-page factors are solid and you have some PR built up. For example, we have many sub-pages on our site that target words that are searched 30-50 times per month. Certainly not exciting numbers of traffic, but that can equate to 5-10 people per month finding your site, and if you have 1000 of these pages, then you can have 5000-10,000 people finding your site for keywords you don’t have to spend a lifetime trying to compete for.
So, another simple question that really doesn’t have a simple answer. In the end there are many ways to become successful in this industry, the only constant is that it takes a lot of hard work.