I'm running Oblivion + Shivering Isles, and patched to 1.2.0.416.
 
Occasionally when I'm in certain rooms, particular areas of the room are black.
 
For example.
 
I walk into a room. It LOOKS normal. I take a few steps forward: It's as if someone turned the lights out.
I can still see my stats, my crosshair, just the room is black.
 
I step backwards, AHA! Light again.
 
Sometimes leaving the room, and re-entering will clear this up.
 
Not a major problem, but has anyone else Seen (or not seen) this prob?

Did you try updating your Forceware Display Drivers?

I'm at the latest on the Nvidia site (169.21)
 
All other drivers, bios up to date
 
XP (SP2)

I'm actually having the same problem!  Well, maybe not IDENTICAL but darn close:  I usually have this problem if I go into Stealth mode, or sit down in a chair.  The screen goes completely black, except for the menus, and if I stand back up, it goes away.  Like you, it hasn't been a big enough problem for me, so I haven't researched it.  

AHA!
 
Yes I forgot to mention that. It happens when I'm SNEEEAAAAAAAKING.

Yes I had this issue, and always when sneaking, annoying but dont know if there's a way to get rid of it
 
A.

jay_l_a, I have similar specs on my rig to yours (same CPU, GPU, same amount of RAM), and I have the same issue.  the only way I've seen to resolve it is to set your interior actor shadows to 0.  It works for me, but I've heard that Oblivion is sensitive to overclocking, so maybe setting your clocks to default frequencies might help?  I may just try that myself.  I believe this is probably a videocard problem, perhaps Nvidia will address it in their next driver update.  Let's shoot them a message describing our problem.

I've had that issue as well, but it didn't really bother me as I experienced it so rarely.

truck pilot, I'll try the internal shadows thing, thanks for the tip.

Have you added any extra weapons or mods lately?

Nope. only thing added is Shivering Isles
 
I haven't had chance to try the shadows thing yet EITHER.
 
But I will.

Same here.  I don't have the expansion.  Usually happens when in 3rd person view inside a confined area.
 
My friend also has the same issue.  He said it is "blindspot".
 
*Shrug*

I'm very experienced in fixing graphical glitches, but Oblivion managed to confound me a couple of times.