I just flashed the stage 1 v1.21 beta base map tonight on my 2004 (09/2003 production) WRX Sedan 5MT. So far so good...even with 91 octane California gas!
Get it HERE
UPDATE: 1 stall this morning (04/13/2005) driving to work. I've flashed the v1.20 base map back and will just keep blipping the gas when I'm braking or before I shift into neutral when coasting until the problem gets fixed.