User Error, Camera Error, Monitor Error? Pictures underexposed!

Hello,

Perhaps some one can help put an end to my insanity.
Background:
I am shooting with a 30d, it's probably about 1.5 years old.
Love the camera, hasn't failed me yet until recently.

The camera was exposing pictures properly on 12/14/08 in my mind.
I put the camera down and shoot again on 12/24/08 and I noticed my pictures are all underexposed.
I've been shooting off since then all all of the pictures are about 1 stop under. What could of caused this?

I just took the picture below 30 min ago.

EXIF
1/50 at 1.4 Lens 50 1.4
Evaluative Metering used.
Shot in raw converted to jpg in lightroom. no adjustments made.

you make sure all your settings are correct? you dont have exposure compensation set to anything other than 0 do you?

ec is set at zero.
i haven't changed anything else, at least intentionally.

I suspect that bright lamp caused the metering to be fooled and underexpose the room a touch.

If you use partial metering off the wall only, I'd bet the metering for the room would be better but the light/lamp would be very very overexposed.