Probably the one thing I've been struggling with more than anything since the change of interface has been how categories are now dealt with.
As was discussed here (but not solved even though the thread is now closed) http://en.forums.wordpress.com/topic.php?id=26503&replies=6#post-190793 is a very similar situation, if not identical to what I have on stusshed.wordpress.com
I have an extensive Category list - I choose to for back-referencing old topics as another way for people to find content on my blog. If I could have a drop down like that for my tags, that'd be good, but it still needs to have the hierarchical structure, so I think categories are still the answer for me.
However, I am finding I am less and less inclined to look at the categories, click (and wait) for the full list to open before scrolling through to check those that are relevant. It would be much faster (as I am finding playing around with Tags), if I could just type the name of the categories I want, and let WordPress tick the right boxes.
I don't want to just use tags, and in fact I'd like to use both. In my case, I'd probably have the tool names (tablesaw, drill press etc) and company names as categories, and the specific actions that the post is actually about as tags. But if assigning categories remains as laborious as it has now been made, I might find myself dropping categories altogether (converting the remainder to tags using the tag converter tool) which would be a real shame.
So again, unless someone can think up an even more convenient interface, I would like to be able to assign tags, and categories in the same way (and if a category that I type already exists (as a category or sub-category) for it to be selected, and if not, for it to be created. Possible? Likely? Please? :)