Check this out:
http://www.ajk.tele.fi/libc/code.html
If anybody's lookin' for a good web interface to libc source code (specifically from NetBSD), the above link is excellent.
I must admit, I've grabbed some code of the site, myself. Personally, I don't want to have to do extensive testing of my kernel's memset routine, for example, if it's only going to get used a couple times... I'd rather grab something that's already been tested by millions of users. Saves a lot of time... not that a memset routine would take long to write, but...
Also, last I checked, all libc's from *BSD and Linux were LGPL, so you could even use these routines in commercial operating systems (although, I think that's kinda lame... if you're gonna be selling stuff, you should write _ALL_ your own code...)
Cheers,
Jeff