I guess my answer is multiple-choice: If your perspective is purely engineering, then I don't see how it matters at all. You evaluate a third-party solution based on the same factors (such as suitability, reviews, reputation, evaluation, and cost) regardless of who's writing the code. Some open source software is garbage. Some commercial (or closed but freely available) software is wonderful. Vice versa.

On the other hand, if open source matters to you as a favorable direction in software development, then you might be willing to engage a little more, do a little more work, report a few more bugs, and even accept a bit more risk, based on your tolerances, because large numbers of people doing those things make open source more competitive and more viable, and then it gets better over time.

@Chris Luebcke: The difference being you can fix open source garbage, but not proprietary junk :-)

Having been a Software Engineer for over 10 years. I would like to add my 2 cents. I work at a company that has used both open source and proprietary products. I have been in the situation where both types of products have reach the End Of Life. For the proprietary solution we had to buy the rights to the source for the proprietary product to keep our product working. For the open source solution we only had to fix problems in the code ourselves now, instead of receive updates. I personally would stick to and recommend Open Source solutions that where based on published specs.

Tom and Dennis, both good points. To Tom's point some (generally smaller) commercial software providers can be quite responsive to end-users' issues, especially in the earlier stages of the product's life. But yes, actually being able to fix it yourself does take some of the edge off when you find a nasty bug--I recently had that experience with a RoR plugin that turned out not to be nearly as actively supported as I thought.