There is room for improvement in the efficiency of using manual trackbacks by two ways:1. Make your posts more generic so that you can trackback to a greater number of other blogs.
The "Top 20 . . . (in your niche)" type posts work great since it looks like you have done a lot of research, thus a lot of trackbacks are merited.
I know this sounds backwards, but you should find the blogs that you want to trackback or comment on, then write the post based on a common theme.
2. Technorati is only one option of locating blogs, but some of them may not even be indexed in the search engines. If you are using trackbacks to get spiders to visit your blog post, then you may want to look for higher ranking blogs that get more frequent spider visits.
I did a test today with Comment Hut to locate higher PR blogs in a niche. I visited each blog it found. In one window I had my WordPress dashboard open to write the post - I jotted notes as I went along in the editor box. I also copied the trackback uri to the dialog box in the post editor.
Eventually I determined a theme - "Best blogs for ATV parts and accessories" which fit the theme of my blog about ATVs. It was a one paragraph post about an ongoing search for ATV blogs.
Over half of the high PR blogs accepted my trackback and I don't think they will delete it. Some of the others should approve the ones in the moderation queue over time.
If I find more blogs related to my post theme, I can add trackbacks at any time by opening the editor window in WordPress.
You can search Google also with a search string like:
trackback+url+OR+uri+blog+comment+October+2007+niche+keyword
Change niche keyword to your actual niche and use a date in the last 30 days to get more recent blogs but not the most recent. This will give you a good selection of blogs to target.
This system will also work with existing posts but you have to ask yourself why would another blogger approve a trackback submitted from a post written a month or two ago?
So to recap, manual trackback linking can be a very efficient WH linking strategy if you gather the urls first and then write the post.