Turn on 800DPI mode for the Logitech MX-510 Mouse

5 easy steps:

1. Get and install the Logitech Applet from here or directly from here

2. Install the poper udev rules:
Create a file logitech-mice.rules under /etc/udev/rules.d/ with the following contents:

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[darkknight@darkworld rules.d]$ cat logitech-mice.rules
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c00e", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c00f", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c012", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c024", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c01b", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c025", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c01d", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
BUS="usb", SYSFS{idVendor}="046d", SYSFS{idProduct}="c031", PROGRAM="/usr/local/bin/logitech_applet -e -s 800"
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Change the file permissions:

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[darkknight@darkworld rules.d]$ sudo chown root.root logitech-mice.rules
[darkknight@darkworld rules.d]$ sudo chmod 644 logitech-mice.rules && ls -l
total 24
-rw-r--r--  1 root root  146 Apr 13 20:30 10-wacom.rules
-rw-r--r--  1 root root 7406 May 21 05:45 50-udev.rules
-rw-r--r--  1 root root  888 Sep  6 23:12 logitech-mice.rules
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3. Modify /etc/X11/xorg.conf as follows to support the thumb buttons:

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Section "InputDevice"
    Identifier  "Mouse0"
    Driver      "mouse"
    Option      "Protocol" "ExplorerPS/2"
    Option      "Device" "/dev/input/mice"
    Option      "ZAxisMapping" "6 7"
    Option      "Buttons" "7"
    Option      "Emulate3Buttons" "no"
EndSection
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4. Create a script xmouse.sh under /etc/X11/xinit/xinitrc.d with the following contents:

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[darkknight@darkworld xinitrc.d]$ cat xmouse.sh
#!/bin/bash

/usr/X11R6/bin/xmodmap -e "pointer = 1 2 3 6 7 4 5"
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This ensures that the scrolling funtion is correctly assigned to the wheel and not to the thumb buttons.

Make sure that the file permissions are correct:

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[darkknight@darkworld xinitrc.d]$ sudo chmod 755 xmouse.sh && ls -l
total 16
-rwxr-xr-x  1 root root 1579 Apr 11 13:43 xinput.sh
-rwxr-xr-x  1 root root   81 Sep  2 17:36 xmbind.sh
-rwxr-xr-x  1 root root   66 Sep  6 23:41 xmouse.sh
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5. Reboot (Or simply unplug/re-plug mouse and restart X)

Happy surfing! Got the udev rules from the Ubuntu Forum (modified the PROGRAM line to use logitech_applet instead of lmctl).

Edit [July 30, 2007]:
It has been a while since the steps above were posted. The syntax of UDEV rules have changed much since then. The updated rule is (for my MX-510):

$ cat /etc/udev/rules.d/60-logitech-mouse.rules
SUBSYSTEMS=="usb", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c01d", RUN+="/usr/local/bin/logitech_applet -e -s 800"

Device details necessary for writing UDEV rules can be discovered using (substitute /dev/input/mouse1 with path to device of interest):

# udevinfo -a -p $(udevinfo -q path -n /dev/input/mouse1)