SharePoint 2010 comes with a bunch of web 2.0 features, tags, tag clouds, rating, social bookmarking and enhanced blogs and wikis. What I really missed in SharePoint 2007 were tags and tag clouds. On the other hand this was a free space for developers like me, see Power Tag Cloud ;-) My experience with SharePoint 2003 already showed that text, dropdowns and lookup columns are too inflexible and people tend to over categorize in the conception stage.