I know this question was posed in 2008, but I can say for sure that a lot of 'molly' is actually MDA, at least in some places. I met a guy in 2010 where I was living at the time who, with not a whole lot of chemistry knowledge, was well known in the area for having produced mass quantities of MDA. They were called 'root beers' to differentiate them from MDMA which wasn't as easy to find at the time.
MDA is not a rare drug. As someone else pointed out, if you're into MDMA and pills then chances are you've had MDA before... it's not uncommon for dealers to sell it as MDMA.
I had my drink spiked with MDA once. The guy who spiked me had just bought several ounces of the stuff thinking it was MDMA.
There are a lot of similarities but the effects are unmistakeably different. MDA is a lot more stimulating and very psychedelic... the visuals reminded me a lot of LSD.