From 'Five Reasons Web 2.0 and Enterprises Don't Mix ' by publish.com:
Opinion: Enterprise-level Web 2.0 apps are coming. But first large companies need to understand the value proposition (not the feel good propostion) of Web 2.0. Are there currently any enterprise-level Web 2.0 apps out there? 1. Zimbra 2. Adobe Flex 3. Microsoft Office Live 4. 24SevenOffice 5. Salesforce, Netsuite
Web 2.0 is hard to define but for me it is about collaboration and organising information more easily. Tags, RSS and mash-up's are good examples. For consumer software (del.icio.us, Flickr etc.) this is easier to implement and getting people to use. Enterprise usage requires more 'what-if' scenerarios and user training (everyone is not as tech-savvy as bloggers who use web 2.0 tools).
24SevenOffice uses Ajax, mash-up's, lets users tag information and in general makes collaboration between users easier.