Quality
Quality management includes the processes required to ensure that the project will satisfy the needs for which it was undertaken.1 Quality also refers to the general standard or grade of something.2
Some argue that you can't get quality if you go open source. In some instances they would be right however over time systems like Drupal have been tested and re-tested to help ensure it is a quality application. Before you assume that quality must be something that is purchased, consider all the proprietary software applications and operating systems out there. How many have never needed a patch or update to correct an issue? Of those few that remain patch-less, how long did it take for that application to come to market? How long did it take for that application to have new features added? It's all about balancing expectations and needs.
Quality Perspectives
To assist your process of defining a quality project and then going forward to implement the quality project, I offer you the following perspectives.
Requirements
The power of an open source application like Drupal is defined by the many features it has to offer. If you assess Drupal based on its ability to "ensure that the project will satisfy the needs" you have a greater chance of delivering a quality product with Drupal than you do with a system that has limited features. Okay, that states the obvious. But what's important to note is Drupal is designed so that you can add custom features, change the existing features, and use the system how you see fit - thus helping to ensure that the project will or can satisfy the needs.
One other point, remember scope creep? It is easy to feel that the more cool functions and features you add to your site, the better the quality. The objective measure of quality is to ensure that all the required needs are met. Of course, if your measure of quality is the number of functions and features that add value to your site, then you will want to define your project as such and incorporate plans to accommodate value-added functions and features.
But can quality be assessed simply by the number of features an application can help you deliver? No, of course not. But from a project management perspective, identifying which features will make the project a quality project is an important step.
Standards
Another side of the requirement coin is often the need to meet a set of standards. Let's divide standards into two categories: industry standards and personal standards.
From an industry perspective, you might have a need for your site to be 508 compliant. In Drupal, this means you need a theme that is 508 compliant. From a personal perspective, you might decide you need magazine quality images and layouts for your site to be considered a quality site.
What ever the standard, be sure to include it in the requirements.
Best Practices
There is more than one way to write code, build user interfaces, and assemble modules for a site. Depending on who you ask you will find people who say "The best way to do that is ..."
With any application, you don't have control over how the code is developed or documented. But with open source you can change the code to meet your needs and your standards. Of course you need to determine whether the results are worth the effort and compatibility issues you will probably have down the road if you do change the code.
For example, if you really think the code that is core to Drupal needs to be changed and you change it, you have probably just created a situation where if you update to the next version of the open source core code. Your site might not function as you originally designed it to if you upgrade. You might also find that contributed modules that are important to your site might also stop functioning properly. Just think about the waterfall effect before making changes to existing and tested code.
Conclusion
Quality is what you define it to be. When dealing with open source applications, you need to deal with the quality of work performed by hundreds of community members. But at the same time, you have thousands of users checking and validating the core and its modules so maybe code quality isn't going to be high on your list of concerns.
So, when managing your projects that use open source, be prepared to deal with quality issues. They will creep up just like with any hand-coded solution you develop.