No, I didn't pre-order it. I used the reserve and pickup option, which is slightly different. It means that they will hold one of their stock for me at the given time slot and if I turn up on time, I am guaranteed an iPhone 6 and pay at the store.
I don't pay for my reservation until on the launch day, but it does mean I get to start in a different queue to the people who are waiting to buy on the door.
EDIT:
It looks like there's been some confusion here.
In the USA, I believe pre-orders can either be shipped or collected in-store as a reservation as soon as stock is available after paying online. In the UK, there is no option to pre-order the iPhone 6 and pick it up in-store. All pre-orders are shipped to the customer's address after online payment.
There is another option where you can reserve an iPhone 6 online and then arrive on the day and buy your iPhone 6 (paying in-store on the day, not online during the reservation stage). For the launch day, Apple Stores in the UK split their stock into two groups: on-the-door stock for the customers who queue up and wait, and reserved stock for customers who don't want to pre-order and wait for shipping. When you set up a reservation for iPhone 6, the Apple Store website will ask you to choose which store you want to go to as well as the configurations that you want. Provided that the chosen item is in stock for the specified store, you can then choose what time you want to arrive and pick up your iPhone. Slots are one hour long and the earliest slot is at 8am.
After visiting a store and consulting a specialist, they told me that on launch day there will be two queues: one for customers with reservations and one for those without. The reservation queue tends to move a lot quicker (approximately 10x compared to the non-reservation queue). If I reserved online and received a confirmation email from Apple, then this means that the chosen store will have my name on a list with a secured iPhone and that I will be guaranteed the configuration I wanted on the 19th, provided that I turn up and pay. They also said that the 8-9am hour slot is just for "traffic management" purposes and that my reservation will not be cancelled if 9am passes before I can enter the store, so long as I visit the store to pick up on the day. If the entire day passes without successful pickup, then my reservation is cancelled and the stock is returned.