Used at my job for managing various Microsoft servers, as well as general helpdesk duties and research. The main system is running Xubuntu 12.04.2 with virtualbox running a VM of Windows XP, 7, and 8. This was built about 2 years ago, so the cpu was top notch then. It's still holding up well for the workload. I have been called upon to do an occasional video edit, and it handled that nicely also.
We use Microsoft Exchange for email, and the Evolution email program is a fully functional replacement for Outlook. Contacts, calendar, tasks, global address book, it's all there. As long as you don't go crazy opening multiple mailboxes and such it is very stable also.
There is a floppy drive in there just because. All of the drives except the SSD were pulled from other machines, including the DVD drives. I do have to make copies of DVD's on occasion, and doing it on-the-fly speeds up the process.
The power supply is the weak link I think. We bought 5 of these at the same time 2+ years ago, and all 5 are still going, but I'm sure it's only a matter of time. My biggest gripe is the cpu power cable is really short. It almost didn't reach even stretching it across the motherboard like this.