Let me begin by saying that I am a Bialetti fan. However, I would recommend that you avoid this particular product. I've used it about 20 times since I've gotten it and only once did I get reasonably equal volumes in the two cups. Usually, it's about 70%/30%, always favoring one particular side. I've tried taking the filter out to see if there were any obstructions, but didn't see any. I've tried heating at different rates but to no avail. Rinsing the top part upside-down under the tap results in equal amounts of water coming out each spout so I know it's not plugged. Eventually I may try crimping the more productive spout a bit in order to constrict the flow in hopes that that will remedy the problem...
Anyway, I usually end up having to pour from one cup to the other to make them roughly equal volumes which is messy. Tonight, the cups were about 97%/3%, which prompted this review. I'm very, very disappointed, however, I'll still probably end up buying a Bialetti 3-cup caffetiera to replace it.
UPDATE, August 30th, 2010: This thing still sucks. I just bought a DeLonghi Espresso machine and it dispenses two equal volume cups. I'm probably going to chuck the Bialletti 2-cup.