I agree that CLAs are a bit of a hassle, but it makes things much saner for licensors and licensees alike. One high profile project that doesn't use them is the linux kernel. It's mostly only the uniformity of mind among contributors that keeps things on course. Can you imagine the consequences if one or more developers decided that they wanted to change the terms for their contributions?

--- scratch that! Ok, I'm a bit out of date: linux's DCO solves this problem without requiring a DCA. But think of other projects that want to have long term growth and what challenges could arise in the face of changing attitudes over time.