I would like entries to have the ability to be assigned to multiple weblogs and their categories.
I do not like using the EE categories as they are - the inability to create nice URLs with them is driving me nuts

I don’t think sharing entries between weblog is really feasible. When you think of weblogs as containers, how can one article be in two containers at the same time? This is what tags are for, I think.

Well, it can be done to a degree with related entries - I guess I am just thinking of anything that would avoid using categories

Well, related articles are just that: a relationship between two articles, a link of sorts. As to your category url problems, perhaps 1.6 has some improvements in this field. Let’s see.

Good stuff - I can almost sense a knowing wink at the end of that “lets see”

I solved this in a dirty way by cloning the article to different weblogs with the clone extension. It’s tricky however, because you only can do this if the categories are the same. So what I do is first assign the same category group, then clone end then switch back. Yes, tricky, but the original categories from the other entries remain intact…

So instead of sharing I duplicate.

Ahhh ok - I have installed that extension and was wondering whether I could get away with duplicating content - but as I have a livesearch as one of the chief ways of finding things it can throw up all duplicates at once in the search results and if content is changed (as it quite often is because they are a large teaching resource) then the content manager needs to edit each entry.
Also my categories are in the main completely different but with a few with shared names.
I really think that the category handling is a little poor for some aspects of their useage - I think think that some sort of variable such as that suggested by Ingmar would help make categories a bit more helpful.