IBM just announced its entrance into the world of Web 2.0 with the release of Lotus Connections , 
announced yesterday at Lotusphere.  They're calling this category 
social software for business and it includes collaboration tools such as user profiles and connections, blogging, shared bookmarks, online communities, shared workspaces, search and tagging.
Clearest indications that Big Blue is getting hip to the ways of Web 2.0:
- IBM has a virtual marketing booth for Lotusphere in Second Life (launching today).
- They're following the "-kr or -zr endings are cool" philosophy by naming a content repository product Lotus Quickr.
It's getting a lot of press coverage, including 
ZDNet and 
BusinessWeek.  The always interesting John Paczkowski  of Good Morning Silicon Valley 
blogs about it here.
This is being billed as an 
IBM vs Microsoft battle, but the IBM offering seems at first glance a much stronger contender to bring collaboration to the enterprise than Microsoft's SharePoint 2007.  Watch this space!