On DevShed today there's a new tutorial that walks you through tips on two things that can help you keep your https site running smoothly and keep in favor with the major search engines - duplicate content and correct 301 redirects.
When trying to maintain a secure protocol on an Apache-based website, you can expect to deal with certain issues, especially if you're also trying to rank well in the search engines. [...] This article provides tips and solutions to help any web developer effectively manage the two most difficult problems in maintaining the secure protocol side of any website. These are the: Duplicate content and 301 redirection from the non-https to http version.
They recommend two things to handle the duplicate content issues: placing a meta tag on the https pages to keep them from being indexed (keeping the search engines from seeing the http and htttps as two different resources, thus two different sites to index) and using a canonical value in a link tag.
As far as the 301 redirects go, they include some PHP code that, if placed at the top of your pages, can detect if the protocol is https or not. If its not, it uses header to perform the 301 redirect.