Lorelle’s comment jump-started my will to look for better WordPress search. After some digging around, I decided that I did not want to change the database structure as that could cause problems with future upgrades. This threw away most of the search plugins out. Currently I am experimenting with the Google Co-op to create a custom search engine. You can search as well as see the search results on the Search page. I will experiment more, possibly with Rollyo and Yahoo! Search Builder. However, these might not be suitable for many businesses and internal blogs.
WordPress 2.2 search will be a bit better because it will support MySQL 4.1 which allows boolean fulltext searches (actually supported by MySQL 4.0.1 and above). However, it will still not search the title, excerpt or the custom fields. Using the custom search engines seems to be the most feasible solution currently. I think that even the default search is acceptable for certain blogs. However, as blogs are getting more critical for companies, they are playing a pivotal role in information creation and sharing. An effective search has become a necessity in such cases.
A more permanent solution I see is if WordPress is able to use external search tools like Nutch or PHPDig. Till then, custom search engines seem to be a good alternative to the default search that WordPress provides. Do comment here on what you think about this.