From Social Patterns
Some people like to browse, others prefer to search, most use a combination of both. And no one ever says to themselves "today I'm going to only browse and do no searching" or vice versa. A person may start by searching for information and then when they find something juicy, begin browsing from there to related to content. Similarly, browsing my lead to search and then back to browsing again.
Providing you users with ways to "pivot" between one form of discovery and another offers them the richest possibilities.
To do so, provide a persistent search box always in the same location (most commonly the upper-right or upper-left of the screen) and when displaying search results, where possible offer related links, "more like this" and other opportunities for lateral exploration.