"To your humble Reg reporter, it's a bit puzzling why anyone would use Numbers for anything other than slick-looking charts, or Pages for ... well ... practically anything"
Well one negative reason for using Pages (or any other non MS Word, word processor) is because just using Microsoft Word for long document editing, if the document contains many references, is likely to result in a hopelessly corrupt document. For years across major releases, if you use the document map at the same time as editing references, you can be almost guaranteed that within a couple of hours of editing your document will reach a corrupted state that cannot print, or randomly loses whole sections of text, or some other document killing ailment. Corruption is less likely to occur when the document map is not being used (as said it is almost guaranteed when editing references and using the document map) but does still occurs far to often. Worse, if it is a long document, the corruption may not be obvious and may (as once happen to me) may end up backed up across all your backup sets. Worse it is more likely to occur the longer your document is, so the more effort it represents the more likely it is to be hit. Worse once you realise it has occurred, Microsoft support documents provide no less than 9, NINE, different methods to try to correct the problem whilst acknowledging it may be that none will actually work (half the several times I have encountered corruption, none did). Worse, this bug hasn't been fixed for several major version number releases of Word (was present on PC Word when I used to use that, is still present on Mac version of Word - I can't talk to the latest PC release of Word).
The fact Microsoft allow a product to be shipped in full knowledge it contains such an issue, is one of the reasons I detest them with a passion.
One positive reason for using Pages is, while it may not be as powerful as Word, overall the new interface is really good, has much less cruft than Word and feels very natural in use. Indeed I would go so far as to say it is a masterpiece (in general structure, if not yet in the detail of some of the features which Apple acknowledge should be improved). If you don't need the additional features Word supports (and few actually do), Pages is in my view now a far better choice. And the collaborative working through the web interface is excellent and renders that old nagging feeling you need to stick with .docx as a base format "just in case" you need to change plan and share it with someone who may not own Pages, irrelevant.
While Numbers, like Pages, has a lovely feel (and I really like how you can define and size multiple tables on a sheet) it is unfortunately, for me, still on the wrong side of the "good enough" divide and I do worry there will be too many occasions when I need the advanced features Excel provides. Plus due to the multi-table on a sheet feature, if you have used it, the export to Excel won't provide a clean equivalent. I use it for documents that I know will remain of limited scope. Excel pivot tables are just too damned useful and powerful to be ignored.