Letter of Invitation?

Sorry I'm posting a crapload in this area but I keep thinking up questions. :/
Anywho, I'm going to have my boyfriend write me out a letter inviting me to stay with him since a lot of people recommend I do this. (Although I'm not completely sure why...) Does anyone have any tips on how that should be done? Does it have to be a certain way?
Also, I'm probably not going to be starting my job as a nanny until I come back from my trip, so on my landing-card should I put "soon to be employed?" Or what would be acceptable? Since I'll be working for a person rather than a company, I'm wondering if her getting what she puts in writing notarized enough to show immigration? I'm probably just over-thinking but, oh well. I'm also on birth control for medical reasons, will this be alright to just keep in purse on the flight?

When my DF wrote a letter of invitation it just included a bit of history about our relationship, previous visits, the basis for this visit, him stating that I would be staying with him in his home and that he would be supporting me financially. He also included his employment details and stated that he was a UK Citizen. He also said he would be waiting for me in arrivals should they have further questions. He formatted it like any other letter.

Regarding your birth control, I always kept mine with me in my carryon and I've never had any problems.

Anywho, I'm going to have my boyfriend write me out a letter inviting me to stay with him since a lot of people recommend I do this. (Although I'm not completely sure why...)

They recommend it because it's on the list of suggested supporting documents for a visitor visa (http://www.ukba.homeoffice.gov.uk/sitecontent/documents/out-of-country/visitors.pdf):

Supporting letter(s) from your friend or sponsor in the UK

If you are visiting a friend, you might want to include a letter of invitation from them as well as their financial documents, as outlined in the ‘Information about your finances and employment’ section above.

You should also consider supplying evidence of their immigration status in the UK.

This could be copies of:
- bio-data pages from their passport
- a valid visa or immigration stamp from their passport
- a Home Office letter confirming permission to stay in the UK

Thanks you guys, he just sent me the invitation letter in an email and I want to know, one, it IS ok to send it through an email, correct? And two, does this sound ok?

"Dear sir/madam,

Amanda will be visiting from America from May 2nd until May 23rd. I have known my girlfriend, Amanda, several years. I have been over to America twice to visit her and she last came over to visit me in October of 2010. The purpose of this trip is to visit England and see my family and I. While Amanda is here she will be staying with myself and my parents. I will be taking some time off from my job so that I can take her places in Norfolk where I live. Currently, I work a job at the *** *** **** and they have agreed to give me time off while Amanda is staying with me. I am a UK citizen and I will be waiting for Amanda at the arrivals in the airport should there be any further questions.

Yours' sincerely, Alex"

I edited out some of the personal details but, hopefully that's good. (he used my name a lot, lol) Should anything be added or taken away? He posted his full address at the bottom of the email as well. Just want to make sure!