Looking good .. I've not found any bugs .. yet!
Seems like you've added most of my suggestions from above .. so thanks for that

.. and all of the bugs mentioned seem to have been fixed .. nice one.
I've a few extra suggestions for you to consider .. for future versions ..
In the links mass edit could we have, for the Apply column, an all select/all deselect tick box (like they do for some vB options)?
Could we also have the same sort of thing for the open/closed radio buttons in the cat admin page?
Perhaps a cat mass edit system similar to the links mass edit?
Again in the mass edit admin page .. as well as the options for open/closed could we have a "hide" option for the cats? (I take it closed just stops people posting new links to cats as it seems you can still click links within closed cats)
A open/close/hide option within the add/edit cat page?
Is there any need to show "My Links" to guests?
When viewing a cat when you hover over the collapse option (nice idea btw) add a mouse-over alt entry .. ie "Click here for simple view" and "Click here for expanded view" depending on the state of the button.
I'll keep playing to see if I can come up with anything else .. but from what I can see this seems stable enough to become the main release