It's been a while since I used Senuti, but I don't remember any problems in finding where it put the songs taken off the iPod, but since I don't remember the details I can't help with that.
But I think there are a couple of easier ways of doing this.
If you're willing to use Terminal, you can enable disk use on the iPod, and open Terminal. Then type:
Code:
cd /Volumes/<your iPod name>/iPod_Control
cp -R Music ~/iPodMusic
This copies your iPod Music folder to your home folder, but the names of the songs are obfuscated. You can add these to iTunes by dragging the new iPodMusic folder into iTunes (this is actually something that's easier in Windows - the iPod's iPod_Control folder is hidden from Finder in OS X, so you have to get the Music folder out using Terminal - in Windows you can navigate to that folder and drag into iTunes directly without the copy step).
Then using the Advanced tab in iTunes, consolidate your music. This will rename the obfuscated files to their proper names and copy the music into the iTunes music folder. Then you can delete the iPodMusic folder.
If you're uncomfortable with Terminal, an alternative is iTunesFS with MacFUSE. This mounts your iPod's music library in Finder and you can drag from there into iTunes. I can't remember if you have to consolidate your music with iTunes, but there's no harm in doing it anyway.