There are several reasons why I've chosen proprietary in the past over open source. There are reasons why I'm running Mac OS X instead of Linux, and why I use the Gimp instead of Photoshop.
First, the price of the software has something to do with it. I can't see spending $100 or more on a piece of software unless it's the OS itself. This is a what I do when I'm not at work, not a paying job. So, if it's a question between a free Gimp, where things are often hard to do, some features are missing, etc. and hundreds for Photoshop, there is no question. I go with free because proprietary isn't affordable.
But, if it's the choice of a sub-$100 program and open source, there are several factors:
1. Does the software have the features I'm looking for RIGHT NOW?
I'm not talking about developers talking about adding the features. I'm not talking about poorly implemented features that they promise to get working well in the future. Can the software do what I want it to do right now? If the proprietary version I'm trying to communicate with is using a protocol and your software is using an outdated/works sometimes or with interaction on their behalf protocol....are you really an option?
2. How does the software LOOK?
Sit down and look at open source vs. proprietary solutions sometimes. Open source software often looks like a flashback to the 80s, while the proprietary is clean, crisp and beautiful. Fonts and UI add to your everyday enjoyment.
3. How easy is it to use vs. proprietary?
I don't want to learn a special scripting language to use a piece of software. I don't want to go through 10 steps to accomplish what I can in one with the proprietary solution. I don't want to have to google and then edit text files to accomplish what reading a prompt and clicking or checkmarking cïan do in a proprietary solution.
These things are all worth money to me. As long as they are, there will be cases where I chose proprietary over open source. I'm not a long bearded, hawaiian shirt wearing activist screaming "Free as in beer". I'm a person who uses his computer to do things and enjoy himself. The easier it is to do those things and the more pleasurable the experience, the more I enjoy myself.