Since everyone else is talking about it...
Google goes after the enterprise customers
with their upcoming suite titled, "Google Apps for Your Domain". There will intially be be a free, ad-suported package that will include GMail, Google's calendar, Google Talk and web site creation software. All of this will be hosted with Google but the small to medium business who decides to use this can brand everything with their own branding and domain names.
Later this year, Google is planning on adding Writely and the Google Spreadsheet to the package, making it more of a direct threat to Microsoft's Office Suite. Google is also planning on marketing this whole package to big, enterprisey companies who would have to pay a fee to use these services. While they may get some takers initially, I don't see this taking off in a big way until it's been out for a few months so Google can work out the kinks and add more relevant business features. It'll be fun to watch how Microsoft handles this though.