I'm a huge fan of FolderShare. It's a great way to automatically share a document library with a group of people, and still have those files available locally when you're offline.
I have yet to install and use Groove (will be part of the next release of Microsoft Office), but it promises the same FolderShare-type functionality for file sharing, but also adds onto that the normal collaboration features that you would use SharePoint for. That is, you will have local copies of discussions, meetings, business forms, and more. When you're back online, everything syncs up so that you get new content, and your new content is pushed to everybody else.
I'm working on a collaborative project right now, and it's a hassle having some things in FolderShare, some things in a SharePoint site, and most discussions in email. I really see Microsoft Office Groove 2007 as being the solution to this headache starting next year.