Gareth, Jim, and I collaborate on a number of topics on any given day. Sometimes these conversations are based on current projects (DemoDayFinder.com, Quirley), sometimes it's creative stuff we plan on pursuing in the future, and other times it's consulting projects.
We had been running a number of different in house tools to manage this constant flow of data. Finally, we decided to take the leap to Google Apps Premier Edition. It offers some features we liked (Postini for instance), and the price was right. Setting up Google Apps on the domain was simple to say the least, and doesn't interfere with other in house systems we continue to run. The system has some hiccups, and it doesn't offer as many options currently as say Zoho, but the on domain services, products in the pipe (Jot for instance), and overall support seemed decent enough. Overall, it a total of two hours to get to a nice working state; keep in mind I customized quite a bit of it.
So far, so good. Creative collaboration never seemed easier.