I have purchased, or rather attempted to purchase twice from DDP. First was in May last year I ordered a walkstool which turned up after about a week or so, so no probs.
Then after I bought the 5D in August last year I decided to get a 28-135 lense for the trip to Borneo to use as a general lense. Ordered from DDP, followed up with a phone call to confirm it was in stock and the order would arrive before we left and was told we have it in stock and it would be sent this week. After 2 weeks, no sign of it so rang again to be told it was on it's way. Rang again with only 1 week to go and was finally told it hadn't left Singapore and they couldn't tell me when it would leave. Gave them a blast and demanded (forcefully) my money back and ended up buying one at the Camera House in Geelong.
Overall not happy with them
This is a bit rich, coming from me, because I am about as much a social media ignoramus as you can imagine... But my understanding, from talking to friends who have had bad experience from some big eBay sellers and whatnot, is that ventilating your grievances on their Facebook sites is actually quite effective. Apparently retailers are quite sensitive about their FB feedback.