Real fast – I was emailed a question like this today about 301′s and categories so I’ll share the method. I say “half dirty” becasue though 301′s are common in SEO some will call it spam or black hat.
This is common to many people, I’m not trying to impress anyone but sometime simple ideas are brought to me by others that make me wonder why I’ve never thought of them.
Anyway… Categories can be used in a number of ways. Many blogs will explain how to use them for PR sculpting, usability or funneling. But, you can use them to help other sites.
If you write a post specifically about another site/post/page elsewhere that you would like to help in the SERPs then write a specific post about it. Title it and make a stong article using all the onpage tools you know.
But also give the post its own unique category, even the same as your title. If you do this on a blog with standing power (you who have one know what that means) then you end up with a few things . First, the indent. A strong blog will be in the index within seconds and most likely the category page will be as well.
Now you have 2 spots. After achieving that then 301 the category url to your target site and re-categorize your post to a new category. You have a page in the serps as well as your target site, but you retain the article content you wrote so you don’t have any disappearing articles.
If you’re no-following your categories or have them roboted out then use a followed taxonomy that works in your blog.