As a webmaster it is only natural to want your website to be on the first page of Google. You also want it to be indexed thoroughly so that your listing on the Google index and on the index of both Yahoo! and BING will benefit as much as possible from thematic linking and keyword density. This is the point at which a 301 redirect can throw up unexpected issues.
A 301 redirect (or a permanent redirect) is a search engine approved means of redirecting one URL to another. An example of this is if, for some reason, you have something like mysiteA.com redirecting to mysiteB.com. Because it is a legit way of redirecting without any penalty the temptation often exists to create redirect chains where one site redirects to another which redirects to something else. There are many reasons why this might need to happen some of which are totally reasonable and a few which are not. Search engines understand that a permanent redirect is a message that the need to redirect is legit but are not so understanding or indeed compliant when there is a redirect chain involved.
As a matter of fact BING announced relatively recently that redirect chains often present crawling difficulties which lead to either poor or non-existent indexing and Yahoo! often has the problem. Google is a little better but even the Google bot has crawling issues when it comes to following every link in a redirect chain. All of this leads to the very obvious solution of using redirects sparingly and only when they are absolutely necessary and then only by rewriting the .htaccess file (for Apache servers). For more information on this you will find the Apache .htaccess Tutorial useful as well as the Apache URL rewriting guide for mod rewrite.