It's highest priority for us for M5 and CR's to finish such guide(current is in draft state and contains inconsistencies).. But actually it should not be complex to try if you already worked with 3.3.x. Basic steps:

• replace jars with new ones from distribution or just change maven pom.xml according to http://community.jboss.org/wiki/HowtoaddRichFaces4xtomavenbasedproject
• upgrade JSF version to 2.0
• remove filter definition from web.xml as RF 4 does not requires it anymore
• go through the pages reviewing components affected by changes in RF 4
  • some was renaimed
  • some still not migrated
    • full list could be easilly explored using readme files in distr(consider that we missed to update before M4 so there are actually components from M4)
    • Also developer reference in a better shape than migration guide - so could be used to check component information(but at some points still in draft)
    • also you could just look into taglib.xml files in ui jar

Probably richfaces-showcase would be also a good start and base reference