I have to add my voice to the apparent minority (on this forum) who are pleased that the NACC has kept Winter Wren for the eastern North American form. My primary reason for liking this decision is simply the conviction that stability is extremely important in English names. This is, as I recall (the 6th edition is at the office...), the first principle listed by the AOU in its policy regarding English names. Stability of English names is at conflict with the policy stated in the 7th edition that both components of a split species should normally receive new names, as this is certainly not a recipe for stability. Fortunately, the AOU has not always followed the 'new names for both splits' policy, not only for splits of 'extralimital' species but also for splits involving a less widespread species, such as the split of Bicknell's Thrush from Gray-cheeked Thrush.
I believe that the idea that 'wisdom begins with putting the right name on a thing' stems largely from the fact that having a name for a thing (whether it is a species, an object or an abstract theory, etc.) allows you to associate the knowledge you have accumulated with the particular thing, and to communicate that knowledge to others. A name for a species serves as a way to file all of our knowledge about the species, whether it is knowledge about natural history, ecology, distribution, physiology, etc. A new name for a species makes that knowledge harder to access, because that knowledge is filed in the literature under the old name, and many people in the future will be unfamiliar with the old name. In the case of the Winter Wren, this name has been in continuous use dating back at least to the 'American Ornithology' of Alexander Wilson, and changing the name risks breaking the link between the bird and the accumulated writings about it over at least two centuries.
Of course, any species split means that the resulting new recognized species are not exactly the same as the 'species' that we thought we knew. But when one of the new splits clearly makes up the majority of the population of the former species, then it is likely better to retain the former species name for the 'biggest' of the new species.
The new Troglodytes hiemalis is not the largest chunk of the former Troglodytes troglodytes, I admit, but it is the largest chunk of the North American forms that have routinely been referred to as 'Winter Wren'. There have been some nods toward the name 'Winter Wren' in Europe, but I don't think it has been used enough to pose a major issue. The official British list admits to the existence of this name as the 'International English Name', but retains 'Wren' as the 'British Vernacular Name'. (I think 'dragged kicking and screaming' sums up their attitude toward such names). In North America, the Pacific Wren does not have a very restricted range, but it seems that it occupies a range maybe only about 50% as large as the Winter Wren.
Changing the English name of a species will cause more confusion when it occurs simultaneously with a change in the scientific name. What reason would a budding ornithologist 10 or 15 years from now have for thinking that a Boreal Wren (to use Joseph Morlan's suggestion),Troglodytes hiemalis, is the same species as the Winter Wren, Troglodytes troglodytes?
The argument that retaining the name 'Winter Wren' for the eastern species will cause problems for records committees in western regions trying to judge reports of vagrants is not very compelling. For a start, the 'hard core birders' who are likely to submit such reports are probably the constituency most likely to be aware of such name changes. Furthermore, it should not be difficult for a committee to put an asterisk beside Winter Wren in a review list to explain that only records of the eastern form are requested, or to immediately reject reports that do not detail how the bird differed from a Pacific Wren.
I do not always agree with the decisions made by the AOU with respect to English names, but I think that in this case they got it right.