The BSD kernels, from all accounts, seem to be stabler, and of better quality than Linux kernels seem to be. BSD kernels are much easier to read and understand. On the flip side, Linux kernels more feature rich, and the quality has improved significantly, seem to perform much better, and better hardware support than the BSD kernels do. Indeed, I’ve heard comments that when it comes to driver support, the BSD’s are where Linux was 5 years ago. I’ll talk more about hardware support below. Personally, the supposed added bugginess of the Linux kernels have not exceeded my threshold of acceptability. And, overall, I don’t think that a Debian box feels any less robust and stable than, say, a FreeBSD box. Of course, the recent spate of holes in Linux kernels are beginning to strain that. (However, we should keep in mind that having more features is a contributory factor: the two latest holes were in the mremap(2) call that is not available for any of the *BSD.)