Jakob Nielsen have since 1996 published the article "Top 10 Mistakes in Web Design", recently updated 2011. At the top of the list we find the mistake Bad Search. It has not always been that way. In 2005 it was listed as number 5, and in 2003 it was not listed at all.
From experience I know it is often much better to search using an external search engine with keywords and the extension
site:theWebSite.com. This technique works on Google, Bing and Yahoo and most likely some more search engines. Problem is that it's probably not known and used as much as it could be. It leaves those users with either navigating the structure on the site or using the web sites internal search engine. If it is bad, the user will probably not find what she wants and move away from the site.
Now, Jakob Nielsen is not the only one expressing the problem with search. Peter Morville, author of Information Architecture for the World Wide Web, says that search is the "worst usability problem on the Web". Still "search" is one of the most used technique to find content on the web. I often see misspelled words that does not render a search result, nor a suggested word list (see example image below). BBC do suggest when I type though.
At the back end professionals struggle to improve search in different ways. Real-time display of possible keywords based on the characters entered in the search textbox is one. Improving ontology and taxonomy is another. Display suggested words when there is no search result, could be yet another way to improve search. But are there more to do to improve search?