If you run multiple blogs on topics ranging from shoes to iPods to food, think twice before you cross-link those unrelated sites since that will not bring any Google Juice to either of you sites and may even have a negative effect.
In response to "I have many different sites. Can I cross-link between them?", Shashi Thakur of the Google Search Quality Team says:
Before you begin cross-linking sites, consider the user's perspective and whether the crosslinks provide value. If the sites are related in business -- e.g., an auto manual site linking to an auto parts retail site, then it could make sense -- the links are organic and useful. Cross-linking between dozens or hundreds of sites, however, probably doesn't provide value, and I would not recommend it.
Now this raises lot of questions. For instance, do we display only those blogs in Blogrolls that are interesting to our readers? What about blog networks like Weblogs Inc. or Gawker or B5Media that cross-link to all their sites in every post ? If Google is not giving enough weightage to unrelated links, let's just hope they are not penalizing sites for cross-linking.