fiance visa or not, that is my question! (Sorry for being lame!)

I have to disagree with everyone who said to just say one is coming on holiday. Why lie to the IO? You are coming to get married, but if you don't intend to stay in the US, there is no visa for that so you are doing absolutely nothing wrong. You can always bring proof that you are setting up home with your American spouse in the UK, eg proof you are expected back at work in the UK, a copy of the UK visa application form. If they got suspcious and searched your bags as they can and do do, and find evidence that you are getting married eg wedding dress, rings, they will have every reason to believe you are lying because you have something to hide (ie you are planning to live in the US but wanted to skip the red tape of a US fiancé visa). They would have every reason to believe that because
1) You lied
2) US fiancé visa takes months to get and involves a medical, criminal check etc so people do try to skip getting it
3) It is possible to switch from visitor to PR spouse within the US (but only if you can prove you married 'on the spur of the moment.')

My opinion: It is very dumb to lie to an IO.

Sorry if I should know this already, but what is the 2 week window thing?

The British consulate now processes spousal visas on an appointment basis ONLY.  The scheduling system (online) is set up with a two week window, so you can only book your appointment two weeks ahead of time rather than just showing up or booking it months ahead of time.

My opinion: It is very dumb to lie to an IO.

I agree that it's dumb to lie to an immigration officer, but I also think that the rules are dumb and are set up to trap otherwise honest people. 

I was terrified about my fiance coming into the US for our wedding.  I didn't know if he was supposed to admit he was marrying a US citizen/resident or if he should use another reason.  Ultimately, after about a dozen calls to US immigration (blech) and the British consulate in NYC, we decided that it'd be best if he didn't mention his intent to marry unless asked outright.  Both outfits are very clear about the situation--as long as there is no intent to stay in the US after the marriage, there is no need for a fiance visa.  However, the mere mention of a wedding is often enough to set off an immigration officer, resulting in someone being detained, interrogated and hassled and, possibly deported if their story isn't judged as believeable by one or two individuals.  The law says one doesn't need a visa in this situation, yet one runs the risk of being deported if they don't have a visa.  Ugh.  The ultimate catch-22.

I know my husband, and I know that if he got carted back to some cell at JFK he'd freak out.  He has a nervous temperament at the best of times and there's no way he'd get through hours of interrogation even though he would be telling the complete truth.  I just couldn't stand the thought of that...having no control over what happens to us.  In our case, it just wasn't worth the risk...he said he was coming to visit my family (hey, he was!) and he scooted through immigration.  He didn't lie...he just answered ONLY the questions he was asked and didn't volunteer any extra info. 

I think ultimately there needs to be some written clarification of this fiancee' visa "loophole".  It's not fair that people can't just say they're getting married and going home without having to endure the hassle of justifying their entire existence to an immigration officer.  I know we need the immigration service, and I appreciate what they do...I just don't appreciate the fact that they make it hard on honest people by setting up a situation in which you are punished for being honest.   

I definently agree about not voluntering the fact that he's coming into the US to get married, even if you plan on living in the UK.

My husband would come to visit me from the UK while we were dating and waiting for the paperwork to get married and live in the US.  He would mention that he was coming to see his fiance and the immigration guys would freek out.  He would have to explain every time that he wasn't getting married and that we were waiting for the paperwork blaa...blaa...blaa... 

I wouldn't outright lie to an imigration officer, but I would offer up the fact you were getting married if you weren't directly asked.