User-level drivers are an approach to improving operating system security and reliability. A critical aspect of user-level drivers is their performance. We've taken a critical look at user-level driver performance both in the context of microkernels (specifically L4) and the more traditionally architected Linux OS.
The project pages are available at NICTA.
I have been involved with microkernel related research for many years. The L4 microkernel was a vehicle for much of this, especially the L4Ka microkernel project.
I was on the SawMill multiserver operating system team at the IBM TJ Watson Research Centre. Unfortunately, the project page is no longer around. Only the publications remain.