A new TechNet article - Best practices for search in SharePoint Server 2010 describes best practices for configuring and maintaining search in SharePoint Server 2010. Personally, practice #4 was new to me
4. Defragment the search database - The search database contains metadata and ACLs of crawled content. Over a series of crawls, the search database can become fragmented. To improve performance of crawls and queries, periodically defragment the search database. For more information, see Database maintenance for SharePoint Server 2010.
More best practice articles are available here: Best practices (SharePoint Server 2010).