My Canoscan N670U scanner, stopped working sometime between Hoary and Dapper (that was some moons ago, paleface). Last souvenir was an horrible screeching noise coming out of the said scanner. But it did used to scan under Windows (98 SE, if you really need to know).
After moving office, installing broadband & Edgy, I decided I would teach this equipment to work, or chuck it.

• Receipes for Canoscan N670U are valid for N676U and LiDE20
• Canoscan N670U scanner is really a Plustek
• Scan with ubuntu is made via xsane, a frontend for sane (Scanner Access Now Easy), shipped with ubuntu dapper (xsane 0.9.9.1, with sane 1.0.18 libraries)
• CANOSCAN N670U scanner works ok with sane as shown here
• they are many ways to configurate plustek backend for use with xsane, but the easiest is to go to this page
• edit /etc/sane.d/plustek.conf this way
  • $ sudo nano /etc/sane.d/plustek.conf),
  • copy & paste code from « Fichier de configuration« 
  • save («ctrl +X» then «y» then «enter»)
• edit /etc/sane.d/dll.d/dll.conf (because ubuntu is a debian flavor, the correct directory is not /etc/sane.d/dll.conf)
  • $ sudo nano /etc/sane.d/dll.d/dll.conf),
  • copy & paste code from « Fichier dll.conf« 
  • save («ctrl +X» then «y» then «enter»)
• Check if the usb scanner recognized by ubuntu (use $ lsusb to scan your usb ports. Canoscan should appear in the list
  Bus 003 Device 001: ID 0000:0000
Bus 002 Device 002: ID 045e:0084 Microsoft Corp.
Bus 002 Device 001: ID 0000:0000
Bus 001 Device 002: ID 04a9:262b Canon, Inc. LaserShot LBP-1120 Printer
Bus 001 Device 001: ID 0000:0000
  I was worried 2 minutes, then changed the usb cable, redid a $ lsusb and all went OK…
  Bus 003 Device 001: ID 0000:0000
Bus 002 Device 074: ID 04a9:220d Canon, Inc. CanoScan N670U/N676U/LiDE 20
Bus 002 Device 002: ID 045e:0084 Microsoft Corp.
Bus 002 Device 001: ID 0000:0000
Bus 001 Device 002: ID 04a9:262b Canon, Inc. LaserShot LBP-1120 Printer
Bus 001 Device 001: ID 0000:0000
• then do $ sudo sane-find-scanner to be sure xsane and scanner can talk together
  # sane-find-scanner will now attempt to detect your scanner. If the
# result is different from what you expected, first make sure your
# scanner is powered up and properly connected to your computer.
# No SCSI scanners found. If you expected something different, make sure that
# you have loaded a kernel SCSI driver for your SCSI adapter.
# Also you need support for SCSI Generic (sg) in your operating system.
# If using Linux, try "modprobe sg".
found USB scanner (vendor=0x04a9 [Canon], product=0x220d [CanoScan], chip=LM9832/3) at libusb:002:074
# Your USB scanner was (probably) detected. It may or may not be supported by
# SANE. Try scanimage -L and read the backend's manpage.
# Not checking for parallel port scanners.
# Most Scanners connected to the parallel port or other proprietary ports
# can't be detected by this program.
• You’re done, run xsane (Applicatione » Images » xsane)
• I still experienced the screeching noise when using the « aperçu » command («CTRL + 1» then «Alt + P»). I will check on this issue later on but until then, my advice is « dont use aperçu« 
• UPDATE : Gerhard Jaeger, maintainer of the plustek-backend above mentionned, « suspect[s] that the current parameterset (which is the same since 1.0.15) makes the device operate nearly the limit, and that there are some devices beyond » [X] and suggests « To fix this, you’ll need to upgrade to [o]ne of the latest CVS snapshots and to compile/install on your own » [X]