You're asking a quite general question, and I'm a little afraid you'll get a lot of 'colored answers'. people's own opinions, but I'll give it a try:
every software has bugs, you can't help that. the real issue is, how does your OS cope with that.. Linux is known for the fact that it doesn't care if a few processes are suck on 100% cpu time all the time, something crashes (like an with an SIGSEGV fault) The kernel just keeps doing it's job, and all other programs just keep running normally.
even if your entire desktop (X) locks up, your kernel keeps running, and the other programs just keep running too. (like your webserver). It's possible to login remotely, and ask your system and kernel what is happening, and what it's doing right now. Most of the time, you'll see an X server taking 100% CPU time, but this doesn't seam to bother Linux at all.
If you compile the Magic-SysRQ key support in the kernel, you'll notice that the kernel keeps registering your keyboard input. (even though X doesn't). "Alt+SysRQ+E, S, U, B" would ask your kernel to tErm processes, Sync the hd, Unmount drivers, and reBoot.
In fact, in the past half year I had my X server locked up 2 times, and I know what I did, and why this happens... and this is the kind of thing I'm not used to. If a lockup like that occurs, I'm stunned like... WHY DOES THIS HAPPEN!! IT SHOULDN'T. Imagine yourself saying that when your explorer crashed.
And, if X doesn't start, I can examine the logs to see why it failed. As a sidenote, I'm running binary-only ATI drivers for my 3d acceleration. linux warns that this taints the kernel, because binary-only drivers can't be tested by open source members... basically my fault. period.
It isn't hard to run bleeding edge software, and yes, trying to update your system every day isn't a good practice.. Logging in as root isn't either. There are really dumb things you could do with virtually every OS making the thing unstable.. If you choose to run the stable software your distro provides, there isn't much that could go wrong. That kind of software is well tested.
A lot of open source software starts as a personal hobby project (a programmer with an itch). Big software projects like apache, openoffice, mozilla, kde are a different story. That software is viewed by many people, and this seams to have a significant advantage. Code that is bad/ugly will be replaced (I never got a change to do something like that on my work), features getting improved, many people work like a thinking-tank, and the amount of people contributing to these projects, theirby improving the software is really impressive.
reliability analysis of linux os
