Let me share a story of the devastating effects changing a domain name and using 301 redirects can have on a sites traffic for several months.
I have a DVD review site that has been running in one format or another since the year 2000. The site itself was reasonably successful and made a fair profit at times. Back in the summer of 2006 the core team on the site decided that we needed to expand in order to future proof the site. DVD as a format probably now has a limited lifespan and we wanted to expand into other areas such as games, music and the new HD formats for movies.
We all agreed that the domain name needed to change as the name was very DVD specific. I was well aware that such a change could have a big impact on traffic, search engine hits etc. so I tried to do everything I could to minimise the hit. I arranged every single page off the old url to redirect to the new site, and I also set the redirects up with proper 301 error messages so that the search engines would know that the pages have moved somewhere else.
I also started going through all of the back links and trying to get those sites to update those links including DMOZ (still pending at...