301 redirects are the recommended method for moving pages, because it tells the search engine to stop looking at the old location. A 302 redirect tells the search engine that the page has moved, but may return to the original location. A 410 message tells the search engine that the requested page has been removed and will never come back, but since most webmasters have never heard of 410, much less know how to implement it, search engines may not handle this properly. A meta redirect does not tell the search engine anything, and may or may not be followed properly.

301 redirects, as long as the page has no links pointing to the original location, should probably be removed six months after the last link pointing to the old location has been deleted. Search engines should only check a few times before removing the URL from their database. However, this is how things "should" work, not how they do. I have had a few pages redirected with 301s keep getting spidered because a certain search engine never updates their index, and others where I was unable to get a link to the old URL changed.

In theory, search engines don't like sites that have a lot of broken links (the spider could see a lot of error 404s as inefficient, and reduce the crawl rate as a result). This is mostly an unconfirmed rumor though. Customers, on the other hand, hate landing on an error message, and if there is a chance that an old forgotten link somewhere on the web could take the user to a non-existent page, they should see a friendly error message that gives a link to the correct place or even better an invisible redirect.

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