There's been a lot of talking about leaky abstractions lately. An abstraction is leaky by definition: it is something simple that stands for something more complex (we'll see later on that this is not entirely true in the fascinating world of physics).
In particular, ASP.NET has been cited some time ago as a leaky abstraction.
These arguments make sense until a certain point. And this point is determined by how much time will the abstraction gain you? The answer with ASP.NET is a lot of time as anyone who's developped web applications with the technology knows.
So the abstraction may be leaky, but it doesn't matter: the really important thing is that it's useful.
Joel's point in his paper was really to explain that at some point you'll need to learn what the abstraction is really standing for because as you use the abstraction in more and more specialized and complex cases, the abstraction will leak more and more. That's true, and the value of an abstraction can more or less be determined by the amount of time you can work with it without having to worry about the complexity that it stands for. Depending on what kind of application you develop, this time can be pretty long with ASP.NET.
Now, what about physics? Well, in physics, there are leaky abstractions, like for example thermodynamics, which nicely reduce the complexity of the chaotic microscopic kinetic energy of molecules to very few variables like pression, temperature or volume. And the abstraction leaks if you start looking at too small a scale, or at a system outside of equilibrium. Still, it's one of the most useful abstractions ever devised: it basically enabled the industrial revolution.
But there are more curious abstractions in physics. If we try to find the ultimate laws of nature, it seems like the closer we look, the simpler the world becomes. In other words, the layers of abstractions that we see in nature seem to become simpler as we go more fundamental. The less abstract a theory, the more leaky it seems, actually.
Could it be that the universe is the ultimate abstraction, the only one that's not leaky?
Well, the point is, the universe is no abstraction, it's reality. But if we're lucky and smart enough, we may someday find the only non-leaky abstraction, the one that maps one to one with the universe itself.