There has been a movement in the CSS design community toward an increased use of unordered lists to contain, well, just about everything. Although this has on occasion been taken a little too far, a very common technique nowadays is to take collections of links (sometimes called menus) and place them inside lists, with one link per list item.
Why is this such a popular approach? There are a few reasons. The most important is that, when you have a list of links, it makes a great deal of sense to enclose them in a list. From the semantic-markup point of view, it's a pretty close match.
From a styling point of view, there are some major benefits as well. Because each list item contains a link, two different elements (li and a) can be styled independently. Since the basis of styling is elements, the more elements you have to work with the better.