Mark, I know you linked to something relating to this tool, but I wanted to reiterate the point for those who are interested. After stumbling around for tools to un-root and re-lock my phone, I also came across the Galaxy Nexus Toolkit.

All I can say is: this is all you need. Given the confusing nature of the rooting world out there, that's the highest compliment I can pay to this tool. It does everything and does it pretty much without any additional interaction.

Lastly, if you're interested, it looks like my Galaxy Nexus has a serious power issue. It always thinks it's charging (which can't be healthy). Other times it can't charge. So I'll be sending it back, and I need to make it look like I didn't do anything bad to it