I took it daily for a period of about 4 - 5 months. It was a low point in my life (about to lose my home, marriage issues, and a whole lot more.) I have to say, in retrospect, it was quite beneficial at the time. I was given anti-depressants from my doctor but I found them so strange that I refused to keep taking them. If you're feeling low, you want to feel happy - mdma does exactly that. As an anti-depressant I found it worked wonders - not exactly 'amazing' but it did work well enough for me to look back and say it was a good thing I did it (at the time)
As as teacher I'd say it was quite easy to establish whether or not it was doing any damage - Everyday I have to lead a class and essentially stay on the ball for prolonged periods of time. At no point could I say "Hey, my brain is fucked/slower than normal." Bear in mind I would take it in the evening (there's no way in hell anyone can teach rolling on mdma!)
I figure it doesn't do any damage as such but (like others have said) it's just not the same when you're taking it continuously, in the space of a few days the real overwhelming feeling of mdma subsides dramatically and doesn't return, even if you increase the dose. (I was averaging 3-4 a night)
The brain needs a lot of time to restore itself and you're certainly not feeling the full effects by a long stretch.
MDMA is best taken once a month, imho.
I haven't taken mdma for well over two years btw.