Thanks for the replies.
1) I get the general impression that that my best bet is going to be to stick to sort by date on the PRS-T1 and then move books manually into collections.
2) I myself use Calibre a lot, tags and all - in fact I'm also using it at the moment to transfer onto the PRS-T1 a few books that I've downloaded from Amazon and converted to ePub. However, the chances of getting Mrs B to even take an interest in, let alone use, Calibre are well below zero. Also, I'm not sure how willing she would be to use the sort function on the PRS-T1. It essentially has to be Collections if I want a peaceful life!
3) I note with interest the following comment by foghat:
Any series you create in calibre will automagically show up in your collection section on the t1.
Could you amplify on this - by series I assume you mean the Series metadata in Calibre. I've got the Kindle Collections Manager plug-in on Calibre but I'd have thought that it works with the Kindle only.
4) I see that there are no comments on the PRS-T1 creating Collections of its own bat - is it just me who has this problem?