Yes, though I don't think you can say anything really objective about the "quality" based on the data available. I found some of the statistics in the case of Windows source indicative of lower readability and maintainability...defined global funcs and structs counts are higher than the Open Source systems (FreeBSD and Linux) and file length is significantly longer, even though Linux is a significantly larger codebase (the largest of all of the systems analyzed). But, of course, that's just numbers...roughly meaningless without context. And, obviously, Microsoft manages to keep shipping code that mostly works, and they hire some of the best developers in the world.
Anyway, while I've never seen the Windows source code, I have looked at FreeBSD, Linux and Solaris, and all are pretty good. I think FreeBSD may be the cleanest (partly because it tries to be fewer things to fewer people than Linux), but probably not technically the most interesting. And, of course, I've only taken a few quick trips through FreeBSD and Solaris, and I've actually written driver code for Linux. Doing real work in a codebase always makes the warts more apparent.
Here's the paper:
http://www.spinellis.gr/pubs/conf/2008-ICSE-4kernel/html/Spi...
And some additional commentary:
http://www.spinellis.gr/sw/4kernel/
Anyway, while I've never seen the Windows source code, I have looked at FreeBSD, Linux and Solaris, and all are pretty good. I think FreeBSD may be the cleanest (partly because it tries to be fewer things to fewer people than Linux), but probably not technically the most interesting. And, of course, I've only taken a few quick trips through FreeBSD and Solaris, and I've actually written driver code for Linux. Doing real work in a codebase always makes the warts more apparent.