NB user namespaces are a fairly new piece of functionality that is still somewhat rough around the edges. You usuaully want to have the most recent kernel.org stable kernel available when using this.
Yes, I confirm it is a little bit touchy for me. gabx@hortensia ➤➤ ~ % uname -a Linux hortensia 3.12.9-2-ARCH #1 SMP PREEMPT Fri Jan 31 10:22:54 CET 2014 x86_64 GNU/Linux I do think my kernel is not too old.
They are broadly speaking functionally equivalent but using libvirt gives you all the usual benefits libvirt has. Stable API, accessible from multiple programming languages, stable configuration, integration with other apps using libvirt. eg you can use virt-top to monitor things or virt-manager as a GUI frontend, etc, etc
Ok, I understand and it is the reason why I decided to stay away from LXC. So, even if it is less user-friendly, I will keep libvirt, as in the past it gave me full satisfaction, the mailing-list tool included :-)