Here's my simple how-to for installing Fluxbox on an N810 with Mer. N800 users may want to stay away, as this disables the built-in keyboard.
1. Install and remove some packages:
sudo apt-get remove osso-xterm
sudo apt-get install fluxbox xterm
2. Make Fluxbox start up instead of Hildon stuff:
sudo rm /etc/alternatives/x-session-manager
sudo cp /usr/bin/startfluxbox /etc/alternatives/x-session-manager
3. Edit some files for usability:
#~/.fluxbox/keys
#Fullscreen button on top and window-switch button on face
F16 :NextWindow
Shift F6 :FullScreen
# fullscreen button, -, and + (in that order); chenges mouse buttons
F6 :exec xmodmap -e "pointer = 1 2 3";xsetroot -cursor_name left_ptr
F8 :exec xmodmap -e "pointer = 3 2 1";xsetroot -cursor_name right_ptr
F7 :exec xmodmap -e "pointer = 2 1 3";xsetroot -cursor_name hand2
#Requires chmodding, not necessary if you don't FUBAR / uninstall all of the Hildon stuff
Shift F7 :exec echo 0 > /sys/class/leds/keyboard/brightness
Shift F8 :exec echo 30 > /sys/class/leds/keyboard/brightness
Control Mod1 Left :PrevWorkspace
Control Mod1 Right :NextWorkspace
# click on the desktop to get menus
#Very nice to not have to change mouse buttons
OnDesktop Mouse1 :HideMenus
OnDesktop Double Mouse1 :RootMenu
#whatever else you want to stick here
! ~/.Xmodmap
! A little strange, but more usable than the default
clear Mod1
clear Mod2
clear Mod3
clear Mod4
clear Mod5
! Top row
keycode 24 = q Q 1 F1
keycode 25 = w W 2 F2
keycode 26 = e E 3 F3
keycode 27 = r R 4 F4
keycode 28 = t T 5 F5
keycode 29 = y Y 6 F6
keycode 30 = u U 7 F7
keycode 31 = i I 8 F8
keycode 32 = o O 9 F9
keycode 33 = p P 0 F10
! Middle row
keycode 38 = a A exclam exclam
keycode 39 = s S quotedbl quotedbl
keycode 40 = d D at at
keycode 41 = f F numbersign numbersign
keycode 42 = g G backslash backslash
keycode 43 = h H slash slash
keycode 44 = j J parenleft parenleft
keycode 45 = k K parenright parenright
keycode 46 = l L asterisk asterisk
keycode 48 = slash apostrophe question question
! Bottom row
keycode 52 = z Z grave grave
keycode 53 = x X asciicircum asciicircum
keycode 54 = c C asciitilde asciitilde
keycode 55 = v V percent percent
keycode 56 = b B ampersand ampersand
keycode 57 = n N dollar dollar
keycode 58 = m M bar bar
keycode 47 = semicolon colon
keycode 20 = minus quotedbl underscore underscore
keycode 21 = plus numbersign equal equal
! Others (backspace, return, etc.)
keycode 22 = BackSpace
keycode 36 = Return
keycode 50 = Shift_L
keycode 105 = Control_L
keycode 60 = period greater bracketright braceright
keycode 59 = comma less bracketleft braceleft
keycode 65 = space
keycode 135 = Alt_L
keycode 108 = Mode_switch
! Keypad, menu, and screen keys
keycode 70 = Tab
keycode 104 = Return
keycode 111 = Up Prior
keycode 114 = Right End
keycode 116 = Down Next
keycode 113 = Left Home
keycode 71 = F16
keycode 9 = Escape
add mod1 = Alt_L
add mod2 = Mode_switch
# ~/.fluxbox/startup
#!/bin/sh
#
# fluxbox startup-script:
#
# Lines starting with a '#' are ignored.
# Change your keymap:
xmodmap ~/.Xmodmap
gksudo nm-applet &
xterm &
#Left and down don't autorepeat by default
xset r 116 &
xset r 113 &
#gksudo /etc/init.d/ssh start &
# And last but not least we start fluxbox.
# Because it is the last app you have to run it with ''exec'' before it.
exec fluxbox
4. Reboot
sudo reboot
You should boot into Fluxbox after that.
EDIT: Added N810 package (eg, compiled with N810 CFLAGS)
EDIT2: Corrected the path for x-session-manager