If we go to wikipedia, here's the description of the flavour of a durian:
"The edible flesh emits a distinctive odour, strong and penetrating even when the husk is intact. Regarded by some as fragrant, others as overpowering and offensive, the smell evokes reactions from deep appreciation to intense disgust. The odour has led to the fruit's banishment from certain hotels and public transportation in Southeast Asia."
Further on in the article it quotes novelist Anthony Burgess as describing "like eating sweet raspberry blancmange in the lavatory", which is more in line with my opinion of it. The flavour descriptions amongst our family ranged somewhere between dry, mango or off lychee to urinal cakes. It's like a smooth, custardy, pungent fruit, but with an almost savoury twist to it as well. The initial taste was the worst - the smell/flavour is really hits you and is very overwhelming - then the flavour improves to almost pleasant, but quickly deteriorates into vile again.
I can tell you as I'm writing this and burping occasionally (oh, the burps are the worst. I'm actually afraid to burp right now) that I can assure you I will never again consume durian smoothie. Even a quick search on flickr will show you that I'm not the only one. My favourite is the one titled Never. Get. The. Durian. Smoothie. And then there's this poor guy. Regrettably, I was in a rush as I was leaving this evening and didn't have my camera or even my phone (it was charging) to capture the moment.
However we did manage finish the durian smoothie. I think this is a decision we are now regretting.