The 2 big sites I am converting to MT from WP have over 100 categories and sub-categories.
Final plans will mean each blog is over 1,000 category/subs on one, and over 3,000 on the other.
The large one is about drive-in movie theaters. 50 states, and the towns/cities that had one or more drive-ins. So, 50 main categories under 'state' category, then each state category has 1-500 sub-categories.
if you want to look at the site before conversion, there be adverts, its url is:
http://www.drivein-jim.net/blog/
Reported on Movable Type 4.2

Sorry, I thought it would auto-link.
link to the pre-conversion blog
Hi Jim, we can't wait to see the new site! Would something like this dropdown navigation make sense for the format you're describing? The downside is that it might require listing all of the possible data in a template, but if that's managed through an include, it might not be a ridiculous amount of text to publish.
Another option is to publish little javascript (JSON) files of the subcategories for each top-level category, and then load them on the fly as users are navigating through the options.
That looks similar to this dhtml menu I use on other sites.
FreeStyle Menus v1.0 RC11
The only problem I see is some states would have 500 entries for sub-categories. Texas is one. I don't remember off-hand but 2-4 other states had over 300 drive-in movie theaters.
That would make for a very long list.
Of course, I could make 'Texas A thru H' and 'Texas I thru L' etc. to shorten them down.
I don't know much javascript, but I'll look over the mootools as well.
Hmm. Yeah, I could use a drop down menu, with links in them to the pages for each town. Might be easier than the other ideas I had in mind.
Well, the new site is here: http://www.drivein-jim.net/newblog/
The maps and aerial photos only show when I click on the one entry that has them, instead of all of the recent ones showing the ropo maps and aerial photos automatically. I havbe 'no hotlinking' turned off in cpanel. So it looks like something in MT.
I still haven't decided on how to do my site navigation.
For now it is done via the category listing on the left sidebar.