I have setup a site using Swipestripe, with Swipestripe categories. My client now wants to re-order their products differently across categories. However every product belongs to multiple categories.

Reordering the SiteTree won't work as doing this will affect the ordering of all the categories a product belongs to (if that makes sense?).

I am thinking that I will have to create another dataobject to manage a category/product/ordering relationship - but I just thought i'd check to see if anyone else has had to solve this problem?

I havent used the module before. but cant you use many_many_extrafields ?

http://www.silverstripe.org/data-model-questions/show/19965

You can use a DataObject which maps to the join table (ProductCategory_Products) - this can be an easier way of managing than extraFields imo. If the client does not need an exact ordering across different categories you might be able to get away with a simple numeric field on Product which is a kind of weighting and then order products according to this value? It depends on whether they have a few products that they want to put front and centre of different categories or if they want a fairly specific order to the products I think.