I'm a big fan of open source software.
Almost all of our client projects are written in PHP and use the standard LAMP architecure. I love open source products such as Wordpress, which despite some flaws is very usable -- especially more recent versions.
Unfortunately, that's not the case for most open source software. Moodle is a case in point. With great functionality, and used by millions of people across the world, Moodle sounds like the perfect open source LMS (learning management system).
Moodle is far from perfect! For example, Moodle homepages tend to have too information, and to be poorly laid out -- cognitively overburdening the user.
Another popular open source system is YaBB (Yet Another Bulletin Board). But it's impossible to create a unique homepage first, and then to plug YaBB in. Instead, homepages for each app look samey and inherit large chunks of HTML. This problem is shared by Moodle.
This shouldn't be the case. After all, these are back end applications. Why should they dictate what the front end looks like?
I could go on (and on). Bottom line: These applications have got usability cancer.
Why are Moodle and YaBB so unusable? Why is open source software, in general, so unusable?
Matthew Paul Thomas has the answers in his article: Why Free Software has poor usability, and how to improve it.
According to Thomas, open source software offers weak incentive for usability; there are too few designers; and design suggestions often aren't welcome or inivited.
Initiatives like OpenUsability seek to address these problems. But considering that Moodle is by far and away the leading open source app in such a popular domain as online learning, I'm afraid open source usability has a long way to go.
Sorry Moodle, but I can't give you the thumbs up until you start making life easier for users -- the course designers, the content creators, and most importantly the students who take courses.