Me - £450 (two orders with the same vendor that never showed up).
Before that I had placed about 100 orders and not lost a cent.
Am sure that will be a paltry sum compared to what some of you have lost.
Edit: I mean in total over all orders, not just in one order.
Something stupid like 0.000026 BTC when one of the markets went (I forget which one but it was last year).
I've been around since SR1 so it's not a bad record!