I have followed this guide for installing the scanner driver:
http://welcome.solutions.brother.com...ion_scn1b.html
And this post:
http://ubuntuforums.org/showthread.php?t=1439450

This has always worked for me on Ubuntu 10.10.
But now on Xubuntu 12.04 it doesn't work anymore. Simple Scan says it couldn't find any printers.
Printing works fine though.

Code:
remco@laptop:~$ sudo dpkg -i --force-all ./brscan-skey-0.2.3-0.amd64.deb
Selecting previously unselected package brscan-skey.
(Reading database ... 224874 files and directories currently installed.)
Unpacking brscan-skey (from .../brscan-skey-0.2.3-0.amd64.deb) ...
Setting up brscan-skey (0.2.3-0) ...
remco@laptop:~$ sudo dpkg -i --force-all ./brscan3-0.2.11-4.amd64.deb 
Selecting previously unselected package brscan3.
(Reading database ... 224882 files and directories currently installed.)
Unpacking brscan3 (from ./brscan3-0.2.11-4.amd64.deb) ...
Setting up brscan3 (0.2.11-4) ...
remco@laptop:~$  dpkg -l | grep Brother
ii  brscan-skey                 0.2.3-0           Brother Linux scanner S-KEY tool
ii  brscan3                     0.2.11-4          Brother Scanner Driver
ii  mfc6490cwcupswrapper:i386   1.1.2-2           Brother CUPS Inkjet Printer Definitions
ii  mfc6490cwlpr:i386           1.1.2-2           Brother lpr Inkjet Printer Definitions
ii  printer-driver-ptouch       1.3-3             printer driver Brother P-touch label printers
remco@laptop:~$ brsaneconfig3 -a name=Scanner model=MFC-6490CW ip=192.168.2.109
remco@laptop:~$ brsaneconfig3 -q | grep Scanner
  0 Scanner             "MFC-6490CW"        I:192.168.2.109
remco@laptop:~$ dpkg -l | grep sane
ii  libsane                     1.0.22-7ubuntu1   API library for scanners
ii  libsane:i386                1.0.22-7ubuntu1   API library for scanners
ii  libsane-common              1.0.22-7ubuntu1   API library for scanners -- documentation and support files
ii  libsane-hpaio               3.12.2-1ubuntu3   HP SANE backend for multi-function peripherals
ii  sane-utils                  1.0.22-7ubuntu1   API library for scanners -- utilities
Also when I start my laptop it says saned is disabled. I don't know if that makes any difference. I did try starting saned, but Simple Scan still couldn't find any scanners.