I've upgraded to Fedora 12 recently... As the binary drivers for my old old old card (nvidia_96xx) are not supported yet (or maybe any more ;-) I've decided to give nouveau a try.

It starts like a charm, but shortly after (a few minutes) everything goes bunkers - fonts instead of being black are light grey or pink ;-), bitmaps are corrupted. In a second I'll attach a screenshot of my screen after about 10-15 minutes.

The kernel (log to be attached as well) is screaming like this:

[drm] nouveau 0000:01:00.0: PGRAPH_ERROR - nSource: PROTECTION_ERROR, nStatus: INVALID_STATE
[drm] nouveau 0000:01:00.0: PGRAPH_ERROR - Ch 1/0 Class 0x0039 Mthd 0x0184 Data 0x000011ce:0x000011ce

My system:

$ X -version

X.Org X Server 1.7.1
Release Date: 2009-10-23
X Protocol Version 11, Revision 0
Build Operating System:  2.6.18-164.2.1.el5 
Current Operating System: Linux sedan 2.6.31.5-127.fc12.i686.PAE #1 SMP Sat Nov 7 21:25:57 EST 2009 i686
Kernel command line: ro root=LABEL=/ rhgb quiet SYSFONT=latarcyrheb-sun16 LANG=en_GB.UTF-8 KEYTABLE=pl2
Build Date: 05 November 2009  07:43:20PM
Build ID: xorg-x11-server 1.7.1-7.fc12 
Current version of pixman: 0.16.2
	Before reporting problems, check http://bodhi.fedoraproject.org/
	to make sure that you have the latest version.

The card:

01:00.0 VGA compatible controller: nVidia Corporation NV18GL [Quadro NVS 280 SD] (rev a2) (prog-if 00 [VGA controller])
	Subsystem: nVidia Corporation Device 0190
	Control: I/O+ Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
	Status: Cap+ 66MHz+ UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
	Interrupt: pin A routed to IRQ 11
	Region 0: Memory at fc000000 (32-bit, non-prefetchable) [size=16M]
	Region 1: Memory at f0000000 (32-bit, prefetchable) [size=128M]
	Expansion ROM at fd000000 [disabled] [size=128K]
	Capabilities: <access denied>
	Kernel modules: nouveau, nvidiafb

As you see lspci claims it's NV18-base card, while the driver says:

[drm] nouveau 0000:01:00.0: Detected an NV17 generation card (0x018a00a3)

Any other data I can provide?