Well, I took the plunge tonight and hacked away at the MT code. I wanted to implement a way to use the blog I've already got to manage the web links on my main page.
First I tweaked the <MTEntries> code as follows (in lib/MT/Template/Context.pm):
Basically, what that does, in addition to being about to use AND and OR to pick the categories for MTEntries, is allow you to limit the categories with NOT, followed by one or more categories to exclude.
For example: <MTEntries category="NOT Links Web Local">
Then I added another MTEntries section to my Index Template for just the Links category.
It's certainly not perfect. This is only my first pass at things, and it is late at night. I'll have to take another look at it later this week when work lightens up a little bit.
The next thing I would like to do is enable something like a nested MTCategories within a MTEntries section. I'd like to be able to get a list of the categories within that group of entries so I could do some kind of heirarchical list of links.
UPDATE: You can download the complete Context.pm file here.
UPDATE AGAIN: Just because I'm lazy, I'll just go ahead and quote myself from the post on the MovableType Support forum:
I hate to reply to myself, but I figured I should mention what I just found out.
Apparently (maybe this is general knowledge, but I was unaware of it), when you limit MTEntries with category, the default days (i.e. taken from the blog config) is tossed out, and any days argument is ignored. I had to use lastn to keep my entire blog (all but the Links category) from being printed out. Luckily, my blog is still relatively new, so there aren't many entries. :)
I've looked through the code and I see where and why all this is happening, but I don't have the time to change things at the moment. I'll probably tackle it tonight.
This looks like any entries that don't have an assigned category are unavoidable excluded whenever exclusion is done. Is that so?