This problem was originally reported here:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/754711

The system works correctly with the Ubuntu-patched 2.6.35 Kernel as shipped with Ubuntu 10.10, but fails with the 2.6.38 kernel from Ubuntu 11.04.

While tracking down this problem, I tested several mainline kernels, all of which also fail to suspend/resume on this system, as I describe below.

Steps to reproduce:
- try to enter suspend mode (I used sudo pm-suspend)

Expected result:
- The system enters sleep mode and upon pressing the power switch, resumes successfully

Actual result:
I tried this with the following kernels (all mainline):

2.6.39-999.201104080911 - The system enters suspend mode, but upon trying to resume, the system is unresponsive: backlight doesn't come on, there is no display, keyboard is unresponsive, and system doesn't respond to pings on the network.

2.6.38-3-natty mainline kernel. The system boots and is usable, enters suspend mode, but upon attempting to resume is unresponsive, the backlight doesn't come up, no display, keyboard is unresponsive and system doesn't respond to pings on the network. At some point I saw capslock flashing but it stopped after a bit.

v2.6.35.12-maverick mainline kernel, with this kernel the system boots but when trying to enter graphical mode becomes unresponsive, no keyboard, network ping or display (screen is black). 

Here is some relevant information on the system, please let me know if any more tests are needed.

dmi.bios.date: 09/08/2009
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A11
dmi.board.name: 0K183D
dmi.board.vendor: Dell Inc.
dmi.board.version: A11
dmi.chassis.asset.tag: 1234567890
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: A11
dmi.modalias: dmi:bvnDellInc.:bvrA11:bd09/08/2009:svnDellInc.:pnStudioXPS1340:pvrA11:rvnDellInc.:rn0K183D:rvrA11:cvnDellInc.:ct8:cvrA11:
dmi.product.name: Studio XPS 1340
dmi.product.version: A11
dmi.sys.vendor: Dell Inc.

GraphicsCard:
02:00.0 VGA compatible controller [0300]: nVidia Corporation G98 [GeForce 9200M GS] [10de:06e8] (rev a1) (prog-if 00 [VGA controller])
	Subsystem: Dell Device [1028:0271]
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 23
	Region 0: Memory at ae000000 (32-bit, non-prefetchable) [size=16M]
	Region 1: Memory at d0000000 (64-bit, prefetchable) [size=256M]
	Region 3: Memory at ac000000 (64-bit, non-prefetchable) [size=32M]
	Region 5: I/O ports at 4000 [size=128]
	Capabilities: <access denied>
	Kernel driver in use: nouveau
	Kernel modules: nouveau, nvidiafb

03:00.0 VGA compatible controller [0300]: nVidia Corporation C79 [GeForce 9400M G] [10de:0866] (rev b1) (prog-if 00 [VGA controller])
	Subsystem: Dell Device [1028:0271]
	Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Latency: 0, Cache Line Size: 64 bytes
	Interrupt: pin A routed to IRQ 18
	Region 0: Memory at aa000000 (32-bit, non-prefetchable) [size=16M]
	Region 1: Memory at b0000000 (64-bit, prefetchable) [size=256M]
	Region 3: Memory at cc000000 (64-bit, prefetchable) [size=32M]
	Region 5: I/O ports at 5000 [size=128]
	[virtual] Expansion ROM at c0000000 [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel driver in use: nouveau
	Kernel modules: nouveau, nvidiafb