Goshdarnit!
I just did something very stupid.
I asked Mathematica to compute a Riemann curvature tensor and print out the out put. But I forgot to tell it to simplify. The result was ... ginormous.
I canceled the job after the 50th page, and the first non-trivial term spanned 5 pages...
Shit. I just came back to the file and now, in print preview, I see that there are 821 pages....
Okay, now that I added the Simplify[] command, the result is down to 8 pages. Let me try that again.