so I had ordered from Apple directly and was waiting for 7-10 delay that's been talked about.
Went and crunched the numbers yesterday. Looked at EE, Three, and O2 and what I would pay over 24 months with a sim-only contract and my iPhone I was going to buy sim-free straight from Apple. I was pretty surprised that a few of the sim-free deals with the carrier were nearly identical to the contract versions and I be paying quite a bit less upfront..
People tend to forget to also factor in resale value - your phone will probably sell for less in 2 years time if it's locked rather than unlocked - if you use one of the phone trade-in companies the difference can be considerable depending on the network. e.g selling an iPhone 4S 16GB on envirofone today:
Unlocked: £115
EE: £65
You can also expect similar differences on eBay etc.
Of course this might not be your intention, or the reduced up-front cost might make it worthwhile for you, but maybe it's relevant to others.