Jason, at NoFunIntended says in Open Source Intimidation:
"There are many smart people out there that want to contribute but can't find the time or just do not have the experience for a bird's eye view of the project architecture."

I can honestly say that there have been several projects I've thought about joining, but it is extremely difficult to find the time, mostly because after I've worked all day, I just want to spend time with my wife and kids.  I did join one project (Easy Trainer .NET), but due to shifting priorities with the project owner (Eric Wise), nothing much came of it.

Don't get me wrong, I do have some of my own projects, both paid and non-paid, that I work on, but those can go at my own pace and I don't have to worry about impacting others (unless of course I'm getting paid for the project).

I've have thought about open sourcing one of my projects (vCard for .NET), but as Jason said,
the "work, after all, is on display for the whole world to see." and I'm not sure I'm ready for that. :-)