I'm not a firm believer of one system to rule them all. But, I can see the attraction from a business standpoint.

If there was a single piece of software or solution that handled all my needs, then yes, it's the best option. Having used Outlook for some time, I would really hate having to use 2 separate programs for my email and calendar or better yet, a 3 program for task management if I actually used Outlooks tasks. I instead, would love to have all those features in one solution that's accessible together.

That means I only need to likely hire one person at the very least versus 2 hires to support both solutions.

When you get into solutions that are a rainbow of different technologies and solutions integrated into a unified solution, then you have what many of you guys run into today. Businesses requiring those one hire to rule them all. The one guy who not only is a DBA, but also a back-end developer and front-end developer who speaks 5 different languages.