Hurray! I finally got around to hacking a little script for vim that will automatically track posting dates for pyblosxom entries. It does the following:

1. For new entries, add '#mdate {currentdate}' on the 2nd line.
2. For existing entries without '#mdate' metadata, it will look up the mdate of the current entry and append it in the form, '#mdate {mdate of file}'
3. After you write (:w, :wq, etc), vim will look for #mdate metadata and turn the date into something touch(1) can use, then set the modification date of the file.

This seems to work pretty well, and is quite transparent to pyblosxom, since it sees lines beginning with #foo as "metadata" - so far so good. However, it does jump to the 2nd line of the file when you save, which is annoying (but fixable). I'll fix that later.

My "vim scripting"-fu is not strong, so there's probably a cleaner/fancier way to do this. Anyhoo, you'll need the following in your .vimrc:

" PyBlosxom stuff
augroup pyblosxom
	autocmd BufReadPost /home/jls/public_html/entries/*/*.txt call Pyblosxom_checkdate()
	autocmd BufNewFile /home/jls/public_html/entries/*/*.txt call Pyblosxom_putdate()
	autocmd BufWritePost /home/jls/public_html/entries/*/*.txt call Pyblosxom_fudgedate()
augroup end

function Pyblosxom_checkdate() 
	" Look in the file for '#mdate foo' metadata
	normal 1G
	let dateline = search("^#mdate")

	" If not found, append the mdate of the file to line 2
	if dateline < 1
		let dateline = 1
		let date = system("stat -f '#mdate %Sm' " . expand("%"))

		" Add the date to the file on line 1
		1put=date
	endif
endfunction

function Pyblosxom_putdate()
	let date=strftime("#mdate %b %e %H:%M:%S %Y")
	1put=date
	goto 1
endfunction

function Pyblosxom_fudgedate() 
	let l=search("^#mdate")
	let l=strpart(getline(l), 7)
	let cmd="date -j -f '%b %e %H:%M:%S %Y' '" . l . "' +%y%m%d%H%M"
	let touchtime=system(cmd)
	let touchcmd="touch -t '" . strpart(touchtime,0,strlen(touchtime)-1) . "' '" . expand("%") . "'"
	call system(touchcmd)
	e
endfunction