With Sitecore 7, indexing is now extremely fast, but if the database is large enough, you may easily end up with
500+ megabytes of disk space occupied by indexes and index rebuild time might still be an issue, as well as a query performance. It might not be a big deal for a global
website search, but if you only use Lucene index to find a few
most recent articles, etc. - this can be an issue.
