I make dozens of small artists' tools out of O1 each year--stock is 1/8" X 1/2" and is Starrett--the "no-name" stuff on sale at Enco was brittle. The tools have two 90-degree bends in them, sort of like those little zed-shaped screwdrivers.
Dennis is right about the quench technique--keep it moving rapidly in the oil until cooled, although I usually hold the pieces vertically in the tongs. Having the oil bath at around 100 degrees F helps too.
Annealing O1 requires a digitally-controlled HT oven, as it must cool down at rate much slower than ordinary "turn it off and leave door shut." The recommended rate varies between 27-50 degrees F PER HOUR from annealing temp (around 1550 IIRC) to 1000-1200 degrees F. My oven cools more rapidly than that, and when I tried to anneal it simply didn't work. Burying the pieces in sand didn't work either.
I did try various normalizing processes (each O1 manufacturer has a slightly different recommendation) but the results were inconsistent--in some instances the pieces became brittle and snapped, and grain growth was visible along the breaks.
There's a stress-relieving technique for O1 some processors advise--heat slowly to 1200 F, then cool in still air. I have tried this, after cold-bending the pieces and before hardening, and it doesn't hurt but I can't tell if it helped.
Here's some links to O1 heat treating. The last one, buffalo precision, has a suggestion for a double temper that they call a "stress relief temper" that really worked for me. After doing the second temper I was able to toss the tools up in the air, and watch them come down on the floor and bounce back up like springs without breaking.
Hudson Tool Steel Corporation
http://www.alro.com/datacatalog/014-toolsteel.pdf
http://www.bucorp.com/files/aisi_o1.pdf
http://buffaloprecision.com/data_sheets/DSO1TSbpp.pdf