It's a poor workman that blames his tools, but I find myself constantly wanting better tools for editing text. I'd like to have Just One Tool for the purpose, but by necessity that must be a plain text editor, or at least an editor that stores in plain text.
While I can use and don't hate software like vi/vim and joe (don't even mention emacs, thanks), I find it difficult to write much more than short notes in those. But somehow those tools just don't do it for me when I want to write a weblog entry. Using those I'm reduced to copying and pasting my text into that shitty little textentry area. The MT4 text interface isn't as terrible, but it's still not great for my purposes, and there's always formatting issues.
I've tried a few pieces of third-party software. I tried Journler but MT4 came out and 2.5 didn't work with it. Now the author's dropped support for weblogging altogether. I don't blame him, but it still stuck me, because I could work around the other shortcomings of the software. What I like about it was the way you can store attachments directly with their individual journal entries, and I'm still playing with it but I'm not optimistic about its long-term viability for my purposes.
After I dropped Journler, I tried some specific tools, Ecto and MarsEdit, but neither of them are good for me either. I forget why I hated Ecto, but I dropped it pretty quickly. I'm writing this post in MarsEdit, but so far I'm not entirely happy. If nothing else, it doesn't yet support tags in MT4.
I looked at using Scrivener, but I can't figure out a way to make it work well for more than a single post per document. There have been a couple of threads on this subject in the Scrivener forums, but none of the suggestions there would seem to be exactly what I want. I'm currently working on a short academic-style weblog posting in Scriv, and it's working out well enough, but I'm not sure how viable it is for managing content for an entire weblog.
Further complicating matters is the fact that I like to write from anywhere. Unlike many people, that doesn't mean I have a laptop I use everywhere. Instead, I have a laptop that I use in places I can't sit in front of a desktop. So, whatever tools I choose needs to easily work on three+ machines, which for me usually means CVS or Subversion respositories. Journler was ok on that front, but MarsEdit and Ecto appear to be non-starters. While Scrivener supports this sort of thing, it doesn't make it terrifically easy either.
At least my three primary machines are all Macs - I shudder to think what would happen if my requirements included Linux or Windows. Nevertheless, sometimes I might like to do things from a non-Mac. MT has the capacity for storing unpublished posts; it would be nice if my tools could store drafts on the server, rather than locally.
It could be that what I'm asking is particular enough that the only tool or toolset that can satisfy me is something I come up with myself. The quest continues.
(Edit: yay, MarsEdit got the correct timestamp, anyway. Boo, my paragraphs were all run together and, of course, it didn't know to ping Technorati.)

(Update 2019-09-01: In the comments on this post originally, Daniel Jalkut, the author of MarsEdit, left some very kind comments and suggested I try an updated version. I did, and that's what I used for the rest of this blawg's lifetime in MovableType/WordPress. Daniel, you're one of a kind.)