Just a follow-up. Got the Datarescue II / Drive Genius package the other day. I had already done a scan of the drive and saved it (to another drive). I checked by doing a new scan to see if anything changed; it didn't. So I went ahead and started recovery of what it could find. The results were all loose files without the correct filenames and directory structure.
A shitload (~10,000 files) of jpegs consisting of both pictures (iPhoto) and what must be browser cache data. An equal shitload of email messages. All of which must be gone thru by hand. Since many of these were already present from the 2/2008 backup, I'm only doing these as needed. I also bought a copy of iLife '08; hopefully the newer version of iPhoto will deal with duplicates better than the version (v4?) I have now. My computer (dual G5 1.8GHz, OSX Tiger) won't run iLife '09, so this is the best I can do.
And a huge amount of iTunes files (23Gb), all of which isn't needed (at least according to my sons who also use the computer).
Things it didn't recover (that I know of): Firefox bookmarks
Pain in the ass, and of course a self-inflicted wound
Another package I looked at that could be better than Data Rescue II is FileSalvage by subrosasoft. This may have a better knowledge of filetypes than Data Rescue does, and has a built-in preview app that seems to work pretty well. Since I already bought Data Rescue, I'm sticking with it and hopefully won't do something stupid like this again.