Reported by Kim Hansen on the Debian BTS yesterday. Applies to intel driver 2.2.0.90. This may be similar to bug#13376 but the symptoms are different (crash instead of lockup).

He says:
"When I configure X for a dual screen setup with a large Virtual display it cashes unless I also turn of acceleration using the NoAccel option.
The crash is immediate for me, it happens when gdm starts X."

His config and log are available at
http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;bug=465421

He sent the following backtrace of the crash:

The hardware is a Toshiba M400.
#0  0xffffe410 in __kernel_vsyscall ()
No symbol table info available.
#1  0xb7d48f15 in raise () from /lib/i686/cmov/libc.so.6
No symbol table info available.
#2  0xb7d4a891 in abort () from /lib/i686/cmov/libc.so.6
No symbol table info available.
#3  0x080a87f7 in ddxGiveUp () at ../../../../hw/xfree86/common/xf86Init.c:1073
	i = <value optimized out>
#4  0x081bae98 in AbortServer () at ../../os/log.c:406
No locals.
#5  0x081bb416 in FatalError (f=0x81c5e9c "Caught signal %d.  Server aborting\n") at ../../os/log.c:552
	args = 0xbf897594 "\v"
	beenhere = 1
#6  0x080c67cd in xf86SigHandler (signo=11) at ../../../../hw/xfree86/common/xf86Events.c:766
No locals.
#7  <signal handler called>
No symbol table info available.
#8  0xb7b41923 in I830WaitLpRing (pScrn=0x8217e88, n=8, timeout_millis=2000) at ../../src/i830_accel.c:120
	pI830 = (I830Ptr) 0x8219828
	ring = (I830RingBuffer *) 0x8229178
	iters = 0
	start = 0
	last_head = 0
#9  0xb7b41a50 in I830EmitFlush (pScrn=0x0) at ../../src/i830_accel.c:217
	outring = <value optimized out>
	pI830 = (I830Ptr) 0x8219828
	__FUNCTION__ = "I830EmitFlush"
#10 0xb7b6c4b8 in I830DRISwapContext (pScreen=0x8227748, syncType=<value optimized out>, oldContextType=0, oldContext=0x0, newContextType=1, newContext=0x8228ff8) at ../../src/i830_dri.c:1153
	pPix = <value optimized out>
	pScrn = (ScrnInfoPtr) 0x8217e88
	pI830 = (I830Ptr) 0x8219828
	__func__ = "I830DRISwapContext"
#11 0xb7f94f57 in DRIDoBlockHandler (screenNum=0, blockData=0x0, pTimeout=0xbf897cd8, pReadmask=0x8206720) at ../../../../hw/xfree86/dri/dri.c:1709
	pScreen = (ScreenPtr) 0x8227748
	pDRIPriv = (DRIScreenPrivPtr) 0x8227ab8
#12 0xb7f93dd2 in DRIBlockHandler (blockData=0x0, pTimeout=0xbf897cd8, pReadmask=0x8206720) at ../../../../hw/xfree86/dri/dri.c:1676
	pScreen = <value optimized out>
	i = 0
#13 0x08090e14 in BlockHandler (pTimeout=0xbf897cd8, pReadmask=0x8206720) at ../../dix/dixutils.c:445
	i = 2
	j = 0
#14 0x081ada38 in WaitForSomething (pClientsReady=0xbf897d10) at ../../os/WaitFor.c:222
	i = <value optimized out>
	waittime = {tv_sec = 0, tv_usec = 0}
	wt = (struct timeval *) 0xbf897cd0
	timeout = <value optimized out>
	clientsReadable = {fds_bits = {0 <repeats 32 times>}}
	clientsWritable = {fds_bits = {138114024, 136760472, 7, 7, 1, -1081508880, 0, 138114264, -1081508544, 226653584, 35, -1210966852, -1210971360, -1214154877, -1214154876, -1214154873, 0, 0, 1, 1142, 136467808, -1209374736, -1214154877, -1210930548, -1214160256, 1, -1208197132, 136476120, -1081508556, -1081508528, -1208275094, -1214160256}}
	curclient = <value optimized out>
	selecterr = 1
	nready = <value optimized out>
	devicesReadable = {fds_bits = {138138760, 138114264, -1081508920, -1214081457, 138114024, 136760472, 138138760, 1, 0, 1, 1, 14, 14, 1, 138114264, 0, 154, 0, 138138760, 136760572, 1, 1, 14, 14, 0, 1, 7, 136148076, 17, -1081508884, -1081507848, 135433476}}
	now = 48517870
	someReady = 0
#15 0x0808cfb2 in Dispatch () at ../../dix/dispatch.c:425
	result = <value optimized out>
	client = (ClientPtr) 0x81e1300
	nready = 16711680
	start_tick = 65280
#16 0x0807470b in main (argc=1, argv=0xbf898234, envp=Cannot access memory at address 0x8
) at ../../dix/main.c:452
	pScreen = <value optimized out>
	i = 1
	error = 136148076
	xauthfile = <value optimized out>
	alwaysCheckForInput = {0, 1}