There's been a lot of talk during this Ashes series of erroneous decisions by the umpires. With every verdict immediately judged against what is suggested by slow-motion replays and Hawk-Eye and the rest of the technology, the idea of the umpire's word being final, while it continues to describe the actual law prevailing, sometimes appears like a quaint anachronism. The umpire's decision can look rather more like an opinion of the moment, and that the first moment only; other opinions soon follow upon it, so that a batsman who was given not out was in fact, we are told, out and vice versa. But in fact as in law the batsman is out or not out exactly as the umpire rules, since the batsman's status is determined by the procedure - that the question is put to the umpire and his word goes.
And yet, being only human, the umpire sometimes makes mistakes, in the sense that his judgement as to whether a ball would have hit the wicket or not, whether a catch was good or not, clean or grounded, can be - objectively - wrong. Do these mistakes matter?
I want to start by saying that, in one significant way, no, they don't. In support of this answer I adduce nothing less than the whole history of Test cricket. For what we know from the errors now regularly turned up by the technology available is, not only that mistakes were made by Rudi Koertzen the day before yesterday and the day before that, and by other umpires on other grounds in other recent matches and series, but that there have always been mistaken umpiring decisions. Not that we needed the technology to know this. It has ever been common knowledge, because it is in the nature of the umpiring situation. What we know now for a certainty, however, is that there must always have been a frequency of umpiring errors more or less comparable to that which the technology confirms there is today. These errors aren't a freak occurrence now, and neither could they have been before - unless one were to maintain, perversely, that the errors only began to occur with any regularity once the technology was in place. I won't pause to take that claim seriously.
So the mistakes don't matter in this precise sense: the entire history of Test cricket has contained them, accommodated them, and it still managed to be the splendid thing it is. Umpiring misjudgements are not some new horror wrecking the game. They've always been a part of it, and yet cricket in its supreme version, Test cricket, has not only survived but has got on wonderfully well. One way of thinking about this is simply to treat umpiring decisions as part of the background context distributing to the two teams the 'luck' that's going: a context which includes the weather, the state of the pitch, which captain wins the toss, which players are available, which injured and so on. In one Ashes series Greg Chappell isn't available to play for Australia; Trevor Chappell is. Not quite the same talent. Another time, Glenn McGrath steps on a cricket ball and is out of the game. Kevin Pietersen, England's most potent batsman, is suddenly sidelined. Again, winning or losing the toss on a good batting wicket can make a big difference. Or a team can be saved from otherwise certain defeat by the weather. It's all just history, and accepted. Just so may one think of bad umpiring decisions.
Note that, in saying the bad decisions don't matter, I do not call upon an argument often used in this connection: namely, that the luck evens itself out over time. (Whatever this is supposed to mean... During the match? The series? A career?) I don't see how anyone can know this. It's not true about life more generally. A piece of what we call bad luck isn't always followed by compensating good luck (although it can be); and some people have more bad luck than others. I imagine that the same holds in cricket as in life. Whether bad umpiring decisions were ever crucial in determining the outcome of a Test match or a series is not something I've ever looked into, but in principle it seems perfectly possible.
In another sense umpiring mistakes also do matter, however. They matter because, once a technology is available that can improve decision-making by the umpires, it is irrational not to use it. What could be the reason for not doing so? Bad luck is bad luck, but bad decisions that are avoidable generate feelings of injustice, and those feelings will be justified if the best effort is not being made. The best effort today must include technological aids that weren't previously available but are now. Provided the technology can be integrated within the rhythms of the game itself, using it to improve decision-making can increase the authority of the umpire, rather than undermining this. But it has to be used intelligently. In some areas - line decisions (run outs, stumpings) - it already has improved things. In other areas - whether a low catch has been cleanly made - the camera sometimes creates rather than removes doubt. As to lbw, Hawk-Eye should perhaps be allowed to 'correct' the standing umpire when it shows either plumb lbw or the ball missing the wicket, but not in the case of anything more marginal. In any event, the players should be allowed to make only a single appeal for each putative dismissal, as has always been so up to now; after that things should be in the hands of the umpires, with those on the field conferring with those who have access to what the technology shows. The system of giving the players an extra but limited right of referral, to challenge first-round decisions, is crazy. It allows some bad decisions to be challenged but not others, and therefore not necessarily the worst ones. For every appeal the umpires should be able to decide on the basis of all of the evidence available to them.
For more on this question, see Mike Brearley here and Gideon Haigh here and here.