I should point out that I was not suggesting that if at least one of my 3 "rules" applies, then the common English name should necessarily be changed. Rather, I said that one shouldn't consider changing the name unless one of the rules applies. Implicitly, I meant that, if at least one of the rules applies, you could consider a name change, but you wouldn't necessarily make it. And if none of the rules applies, don't even go there!
The "really inappropriate" name examples are real, which may not be obvious to European birders: some years back the AOU changed "Wood Ibis" to "Wood Stork" (it is a stork) and "Upland Plover" to "Upland Sandpiper" (it is considered a sandpiper). I have mixed feelings even about this, but it does seem pretty bad to imply through the English name that one particular stork or sandpiper is in a different family, so I can go along with it. These are cases of a single species being given the typical name from a family to which it doesn't belong; they are different from Peter's examples - storks are generally called storks, not ibises. Most American sparrows, though, are generally called, well, sparrows, as "inappropriate" as the name may be. In each of Peter's examples we're dealing with many species, and the inappropriate name is generally the result of a group of American birds having been given the name of European birds that looked similar to "early American birdwatchers". And of course the case of "redstart" for Myioborus is somewhat analagous - a group of birds was given the name of other birds of spurious taxonomic proximity.
Rasmus, I'm well aware of the constantly evolving taxonomy of neotropical birds. This to me is an added argument for NOT changing English names when no taxonomic split/lump/novelty is involved. There's no need for any more confusion, thank you very much.
I'm also well aware that SACC stands for South American Checklist Committee - I enjoy reading their discussions on their web site. (Like you, though, I found their decision to change Lulu's TT to Johnson's very dubious indeed.) But to return to the discussion at hand, surely we don't want the Myioborus species that occurs on both sides of the Panama-Colombia border (Slate-throated) to have one name for North America and a different one for South America! And the AOU, rightly or wrongly, has had "redstart" as the name for Myioborus since they extended their coverage to south of the Rio Grande, if I'm not mistaken.
What's in a name? Or, in this particular case, what's in a bird name? Ideally:
1) a handy label that people can use and have understood without confusion
2) for the poetically-inclined, a word that has some beauty, charm or "memorableness"
3) something that imparts information about what it refers to.
I guess for me 1) and 2) are more important than 3) - my ordering was not a coincidence!
Finally, Rasmus, I suppose you could convince me that almost as many serious birders go to Ecuador as Costa Rica. But what about casual birders? Surely far more ecotourists go to Costa Rica than to Ecuador. And surely some of them buy the bird field guide?!