Well, no, but I think it's worthwhile to first stop for a moment and consider what we mean by "useful" in this context. Scientific principles are useful to us because they illustrate or illuminate some aspect of actual reality. Whatever else it may be, science is not a solipsistic exercise, and is predicated on the assumption that objective reality exists beyond ourselves. Given that, for our principles to be truly useful in a scientific sense, they must then bear some relationship to objective reality, and hence be in some sense, truthful, albeit as an imperfect approximation of truth, rather than being provably and indisputably true. The inverse-square law of gravitation is not deductively and provably true, but it is useful to us precisely because it appears to bear some relationship to the actual, objective behavior of physical objects. Insofar as that behavior objectively exists and is objectively real, the inverse-square law must then be at least an approximation of that objective reality, else we would not find it useful. And it seems to me that the better those approximations are, the closer they are to that unnattainable objective truth, the more useful they then are in a scientific sense - i.e., there are degrees of usefulness which correspond in some sense to the principle's correspondence with external reality.
This should not, of course, be taken to mean that "useful" and "true" are equivalent, or that "useful" even necessarily implies "true" in all cases. But I think it's clear that the principles we find useful are useful precisely because they represent some approximation, whether near or far, of actual reality, and hence, truth. When someone is sent up for trial, we expect the state to prove its case, that the defendant is to be proven guilty. Clearly, however, we do not expect the state to conclusively prove its case true as a matter of logical certainty. Instead we expect proof beyond a reasonable doubt, proof as a matter of reasonable certainty rather than absolute certainty - after all, no matter how good the prosecutor is, he or she can never eliminate as a matter of certainty the hypothesis that Nicole Simpson was killed by Colombian drug dealers or Martians or Santa Claus or whatever.
Instead, it is "proof" in an inductive sense that we seek, not proof in the absolute deductive sense. And I think this is the sort of proof that science is generally concerned with, where we examine where the bulk of the evidence rests, and when the evidence overwhelmingly lies in one particular direction, we then reasonably conclude that the issue is, at least for the moment, proven as a matter of reasonable certainty. Which we can do precisely because we don't restrict "proof" to mean "unassailably true" most of the time. In fact, by "proof", we usually mean "reasonably certain", and it's hard to see how it can be any other way - if we reserve the word "proof" for only those situations deductively demonstrable, we will probably tend to find that the word "proof" has ceased to have much utility for us at all, having no real application to any circumstances beyond the purely hypothetical.
It is certainly fair to state that the theory of evolution is not conclusively proven true, but I do not think it is at all unreasonable to state that, at least for the time being, it is proven as a matter of reasonable certainty. The theory of evolution is not expected to be taken axiomatically, after all - we consider it to be true because that is the direction in which the bulk of the evidence currently points. In the sense that it then illustrates some aspect of objective reality for us, it is both useful and reasonably true.
Bingo - a practical usage of proof.
You too, eh? "Useful" is an adequate distinction to operate on. TRUTH, like "Proof", is in the eye of the beholder. Please consider what you have just said here about the inverse-square law: it is useful to us because "it appears to bear some relationship to the behavior of objects". That's all you need to know--that the inverse-square law can be useful in landing spaceships and predicting eclipses and piecing together what it must look like in distant regions of space. TRUTH need not enter the picture, unless your religeous, or religeous-like convictions incline you that way. Utility is a pretty obvious telescope whose view looks pretty similar for every sane observer--TRUTH is a fractured kalaidascope every viewer can put together in his own peculiar way, and arrogate to his own peculiar agenda.
I see, you think what lawyers say about this word should carry the day. So, if 51% of the evidence points to one conclusion in natural science over its opposite, then it is proved? 81%? 91%? One day it was 99.98 percent certain, and it wasn't proved, but the next day it was 99.99 percent certain and it was proved???? If we reserve the word "proved", when we are talking about technical issues, to tangible deductive proofs, it will still have meaning, I feel relatively safe in claiming.
I also feel relatively safe in predicting that scientists are not generally going to be tongue-tied if deprived of a degerate misuse of the word "prove". We cannot prove things in science, we can increase our confidence in things. Which is good enough--there is no need to oversell our ideas with false claims about "proof", that make us particularly vulnerable to attack by creationists and ID'ers, with an audience that isn't going to mull over the odd metaphysics of a lawyer's version of "proof" for half a day before voting to let ID into the classroom.
I'll repeat the question my other deponent here did not effectively answer: it is a truism of scientific rhetoric that scientific theories are subject to question. Now you've claimed that the best scientific theories are "proved". So what "proved" means, is "subject to question"? I guess a word means whatever you want it to mean.
let me just pass on some advice from God about this. "Do not follow a mob to do evil". Just because something slipshod is a relatively common practice, doesn't make it an acceptable thing. Practically everybody watches television. That does not automatically make a television a virtuous device.