Customs was a breeze!
We got to London around 5 and had to circle until we could land at 6 - we were the first plane to land for the day so customs was empty and such a breeze to get through. I handed him my landing card and passport and the conversation went like this:
Customs Agent: Business or Pleasure
Me: Pleasure
CA: What are your plans?
Me: visiting my boyfriend and other friends
CA: How long have you known him?
Me: We met in 2005. He wrote a letter inviting me.
CA: Can I see it?
[passes letter]
CA: When are you leaving?
Me: December 22
CA: Okay, enjoy your stay. [stamps passport]
I know you're not supposed to offer extra information to them, but from the look on his face, I could tell he wasn't overly excited that I was visiting my boyfriend for so long so I figured I would mention the letter.