MadPenguin has a review/article about how to install and setup Ubuntu in a Business enviroment.
The two-page story begins here.
I won't go into reliability and security here. I've had no security or spyware problems with either Windows or Linux, but I've certainly screwed up my fair share of Linux installations experimenting with software not in the official repositories. Any computer can be safe if you know how to manage it, and a disaster if you don't. Plus, many of these features relate to free operating systems in general. Not just Ubuntu… and not just Linux.
Speaking for myself, my productivity at work has increased since I ditched Windows. In part because of the highlight/middle-click to copy/paste thing. I know it's small detail but it's a good one! Ubuntu has done alright by me, so far, and has spread backwards off my desktop onto many of our development servers. If Canonical continue to succeed in their campaign for enterprise accreditation, things are only going to get better.