Full contents of xorg.conf, Xorg.0.log, dpkg -l, dmesg at
http://web.hexapodia.org/~adi/farthing/bugs/20090109-nv-hang/

I have a Dell Precision T3400 running Debian Lenny with:

ii  xserver-xorg                        1:7.3+18            
ii  xserver-xorg-core                   2:1.4.2-9           
ii  xserver-xorg-input-all              1:7.3+18            
ii  xserver-xorg-input-evdev            1:2.0.8-1           
ii  xserver-xorg-input-kbd              1:1.3.1-1           
ii  xserver-xorg-input-mouse            1:1.3.0-1           
ii  xserver-xorg-input-synaptics        0.14.7~git20070706-3
ii  xserver-xorg-input-wacom            0.7.9.3-2           
ii  xserver-xorg-video-nv               1:2.1.10-1          

X starts up fine with one monitor attached (I have two Dell 2007FP), but with the second monitor connected startx hangs (mouse pointer moves, and it's run some things out of .xinitrc, but no CapsLock or NumLock or C-A-Backspace) with the following in Xorg.0.log:

(II) NV(0): Serial No: C953684U2A2S
(II) NV(0): Monitor name: DELL 2007FP
(II) NV(0): Ranges: V min: 56  V max: 76 Hz, H min: 30  H max: 83 kHz, PixClock max 170 MHz
(II) NV(0): EDID (in hex):
(II) NV(0):     00ffffffffffff0010ac20a053324132
(II) NV(0):     121201030e291f78eeee91a3544c9926
(II) NV(0):     0f5054a54b008180a940714f01010101
(II) NV(0):     010101010101483f403062b0324040c0
(II) NV(0):     13006f131100001e000000ff00433935
(II) NV(0):     3336383455324132530a000000fc0044
(II) NV(0):     454c4c203230303746500a20000000fd
(II) NV(0):     00384c1e5311000a2020202020200028
(--) NV(0): Trying load detection on VGA0 ... tossed event which came in late
mieqEnequeue: out-of-order valuator event; dropping.
tossed event which came in late

connecting with GDB I see this:
0x00007ff9d0764d3a in G80DacLoadDetect ()
   from /usr/lib/xorg/modules/drivers//nv_drv.so
(gdb) where
#0  0x00007ff9d0764d3a in G80DacLoadDetect ()
   from /usr/lib/xorg/modules/drivers//nv_drv.so
#1  0x00007ff9d0769ec1 in G80OutputPartnersDetect ()
   from /usr/lib/xorg/modules/drivers//nv_drv.so
#2  0x00007ff9d0764bbd in ?? () from
/usr/lib/xorg/modules/drivers//nv_drv.so
#3  0x00000000004b2d05 in xf86ProbeOutputModes ()
#4  0x00000000004b994c in ?? ()
#5  0x0000000000527d3b in RRGetInfo ()
#6  0x000000000052beb5 in ProcRRGetScreenResources ()
#7  0x000000000044f7d2 in Dispatch ()
#8  0x0000000000436bd5 in main ()


I can workaround with the following:
1. unplug second monitor
2. start X (comes up to desktop)
3. plug second monitor
4. xrandr -q # shows VGA1 as first monitor, VGA0 as second, probe works
5. xrandr --output VGA0 --auto --right-of VGA1 # second monitor comes up
(6. restart fvwm because it loses its brains when xrandr adds a new pipe)

I glanced at http://cgit.freedesktop.org/xorg/driver/xf86-video-nv/log/ and don't see anything that looks likely to improve the situation post-2.1.10, but would be happy to be pointed at a likely fix.