Computers and indexing algorithms are inherently stupid. If the Web developer misspells a word, it is entered as such on the database. If the searcher issues a misspelled query term, that is what is searched for. So, recognize that computers are stupid and guard against these mistakes yourself. Sloppy entry of query terms will cause you time and frustration.
Redundant Terms Think of constructing a query as being in a card game.
If the answer is yes, pick the term at the appropriate level and discard the other one. These words, and others like them, are not always ignored. It appears that at high-demand search times that some of the engines choose to ignore processing them. Should you experience such behavior, one solution, if you indeed need to use such ignored terms in your query, is to make sure that you place these words in quotes or make them part of a phrase. The ignored behavior appears to be limited to use of such terms as individual words in queries, and then only at some times of the day.