I can see how many visitors they get a day, entry and exit pages and a wealth of other information. If you are not careful, I'll find my way into your site stats as well. Viewing the source code tells me a lot about the page, the meta tags, the experience of the coder, software used, maybe when it was made. For now, lets save it for a closer look. Brett Tabke has put together a great set of tools here.
First step is the Web page reputation calculator.
This tells us what keywords are being linked to our target web site from external sites. Relevancy is the key here. While a big fuss is made of links, what is not so commonly known is that a great deal of easy to get links may actually degrade your ranking. Just use the tools, see what happens. You will soon find that getting a top ranking on your chosen key word may not be such a tough job after all.