Be aware, you don't get a new warranty on the replacement, it still uses the previous warranty of the PSU you returned, so you have ca 6 months warranty on the new PSU. Make sure you test it thoroughly soon.
I've had 3 Corsair PSU RMAs so far, all have been quite painless indeed. However, it's always better if you can go back to the retailer as postage costs are a lot less and if they also send out new units, turnaround will be quicker. Under the Sales of Goods act, your contract for the warranty is with the retailer and not the manufacturer, so technically the retailer should replace it themselves for the whole duration of the warranty. Any experts can correct me if I'm wrong, but this is my interpretation. OcUK say they will cover the warranty for the first year, but I believe they must cover all of it if you ask, as they are the retailer and your contract is with them. This may be of some use to people who are finding the postage costs to the netherlands quite unpalatable. I also fired off an email to Corsair support on my 3rd PSU RMA and they took care of the postage cost for me, so they're a very good bunch and despite the issues I've had with some units, I'll still keep buying them as the product is great and support is even better.