After far too much pain and suffering, I got my tablet to work again. Culprit: the switch to an ATI graphics card threw my config out of whack.

Section "ServerLayout"
        Identifier     "Default Layout"
        Screen      0  "aticonfig-Screen[0]-0" 0 0
        Screen         "aticonfig-Screen[0]-1" RightOf "aticonfig-Screen[0]-0"
        InputDevice    "stylus" "SendCoreEvents"
        InputDevice    "eraser" "SendCoreEvents"
        InputDevice    "pad"
EndSection

Section "Files"
EndSection

Section "Module"
        Load  "glx"
EndSection

Section "ServerFlags"
        Option      "DontZap" "True"
        Option      "AutoAddDevices" "False"
        Option      "Xinerama" "on"
EndSection

Section "InputDevice"
 Identifier  "cursor"
        Driver      "wacom"
        Option      "Mode" "Absolute"
        Option      "Device" "/dev/input/wacom"
        Option      "Type" "cursor"
        Option      "USB" "on"                  # USB ONLY
EndSection

Section "InputDevice"
        Identifier  "stylus"
        Driver      "wacom"
        Option      "Mode" "Absolute"
        Option      "Device" "/dev/input/wacom"
        Option      "Type" "stylus"
        Option      "USB" "on"                  # USB ONLY
EndSection

Section "InputDevice"
        Identifier  "eraser"
        Driver      "wacom"
        Option      "Device" "/dev/input/wacom"
        Option      "Type" "eraser"
        Option      "USB" "on"                  # USB ONLY
EndSection

Section "InputDevice"
        Identifier  "pad"
        Driver      "wacom"
        Option      "Device" "/dev/input/wacom"
        Option      "Type" "pad"
        Option      "USB" "on"                  # USB ONLY
EndSection

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-0"
        Option      "VendorName" "ATI Proprietary Driver"
  Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"
EndSection

Section "Monitor"
        Identifier   "aticonfig-Monitor[0]-1"
        Option      "VendorName" "ATI Proprietary Driver"
        Option      "ModelName" "Generic Autodetecting Monitor"
        Option      "DPMS" "true"
EndSection

Section "Device"
        Identifier  "aticonfig-Device[0]-0"
        Driver      "fglrx"
        Option      "OpenGLOverlay" "off"
        Option      "OverlayOnCRTC2" "1"
        Option      "DesktopSetup" "clone"
        Option      "VideoOverlay" "on"
        Option      "EnableMonitor" "crt1,tmds1"
        BusID       "PCI:1:0:0"
EndSection

Section "Device"
        Identifier  "aticonfig-Device[0]-1"
        Driver      "fglrx"
        BusID       "PCI:1:0:0"
        Screen      1
EndSection

Section "Screen"
        Identifier "aticonfig-Screen[0]-0"
        Device     "aticonfig-Device[0]-0"
        Monitor    "aticonfig-Monitor[0]-0"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes    "1600x1200"
        EndSubSection
EndSection

Section "Screen"
        Identifier "aticonfig-Screen[0]-1"
        Device     "aticonfig-Device[0]-1"
        Monitor    "aticonfig-Monitor[0]-1"
        DefaultDepth     24
        SubSection "Display"
                Viewport   0 0
                Depth     24
                Modes    "1280x800"
        EndSubSection
EndSection

I also had to manually calibrate my Wacom tablet.

xsetwacom set pad StripLDn "CORE KEY  Minus"
xsetwacom set pad StripLUp "CORE KEY  Plus"
xsetwacom set pad Button4 "core key  Del "
xsetwacom set pad Button3 "core key space "
xsetwacom set pad Button2 "CORE KEY n"
xsetwacom set pad Button1 "CORE KEY p"
xsetwacom set stylus Screen_No "1"
xsetwacom set stylus topy "361"
xsetwacom set stylus TopX 29500
xsetwacom set stylus BottomY 22000
xsetwacom set stylus TopY 0

Last bit of weirdness: the pad buttons only work if I’m also touching the scroll strip. It took me ages to figure that out.