Used them once, never again.
In October 2009 I ordered two lenses online on the 18th. On the 22nd I emailed to see where they were as they had debited my card, only to be told they were expecting to receive my order in the middle of the following week. On the 23rd I requested them via email to cancel the order and refund me, and to acknowledge and confirm this request. In reply they explained the reason my card was charged was "when you go online you go through paypal who have to verify your card and do security checks." I paid by credit card. They completely ignored my cancellation request, saying they'll email when the items arrive.
Three days later I get an email saying one of the lenses had been dispatched (I'd already asked to cancel the order, remember) and that they'd refunded the cost of the other lens onto my card, with a note saying "Refund may take a few days to show up". Turns out 'a few days' was very optimistic. Two weeks later, still no refund. Cue another email, this time the reply was along the lines of "the refund was definitely sent, have you checked with the card company? Maybe the bank overlooked something". Right, of course, that'll be it. I had an email later that day, here's what it said:
Now, I don't know about you, but somehow that doesn't quite have the ring of truth about it.
Like I said, never again.