At Knowledge 15, britt.champeau put together a lab guide covering everything you need to know about moving from Knowledge Management v2 to Knowledge Management v3. I've attached a PDF of that guide. All appreciation should be targeted at her because I'm just the messenger.

If you couldn't make it to her session at K15, she covers:

1. New menus and modules
2. Configuring portal properties
3. Creating user criteria to limit viewing and editing content
4. Creating multiple knowledge bases
5. How to create categories within new knowledge bases
6. Migrating content
7. Creating new articles that require approval or are instantly published

You may be particularly interested in Section 6 because it talks specifically about migrating content.

The information is presented as a lab guide. We aren't providing a lab environment along with this information, but you can use the information in your sub-production instances before going live. For more information on migrating to KM v3 see All things Upgrade considered on Knowledge v2 to v3 and Step-by-step guide to Knowledge administration and usage

If you have any questions leave a comment, or if you have praise for Britt, be sure to @mention her and say thank you.