If it makes anyone feel better, I haven't seen an increase in actual sales numbers, but I HAVE noticed a whole lot of customers using DC to pay for their purchases. Even my existing customers have used DC once it became available, when they had paid using PayPal in the past.
The only real advantage to DC is the use of Etsy Gift Cards, but (a) I don't know a single shop owner who's had an item paid for using an Etsy Gift Card (and I know a few shop owners with over 5000 sales each) and (b) I have never had anyone redeem a GC in my shop either. But with the holidays coming up, people might start getting some EGCs in their stockings...so who knows?
Direct Checkout fees are much higher than PayPal's, so that's a real pain the butt - but giving customers the extra option just makes for a better sales experience, I think.