Linking to your website is one of the most misunderstood concepts about internet marketing. What links do you need? How many links do you need? Can I have too many links? Why are links good? The answer is pretty simple. If the website that is linking to you has relevance to your website, it is a good link. If that website has authority, meaning it is well respected (Wikipedia), then it is an especially good link.
The Restaurant Analogy
Let's pretend that your website is a restaurant instead of a website for just a minute. We'll say that you have an Italian restaurant that gets about 50 patrons every Friday night. If a few of these 50 patrons start talking about your food to all of their friends, your business may go up over time. Some of these patrons may be foodies and have good knowledge of Italian food, and others may be known for ordering mac & cheese. Either way, most of these recommendations are good and they will add up over time.
Now let's say that Wolfgang Puck visits your restaurant and tells a local paper that you have the best lasagna in the city. Obviously his recommendation will carry a lot of weight, and your business will skyrocket. That is what happens when you get very high-value links to your website. Juggernaut websites that are well respected can give your site a lot of clout.