vacation, in the uk

 I  want to visit my girl in the uk, we have been talking for 6 months now and talked about me moving to the uk to be with her, but before we do that we want to visit for a while, if i was to go visit for a month would there be any problems, with immigration etc... or should i make it a shorter trip.would really appreciate any advice.

you get your passport yet?  You dont need a visa to visit, I went for two weeks last May, my first trip over to see my now husband.  I had a round trip ticket, the IO asked me why I was there and I said to visit my boyfriend and he told me to have a great vacation!  If its your first time over and you have r/t ticket, I dont think its a problem.  When they all wake up you'll get some more replies here!   Good luck to you!

You can visit for up to 90 days on a return ticket without anyone batting an eyelid

Moving this to the visas section. Immigration will often bat an eye lid on this kind of thing, and it isn't as easy as it sounds. I did the same thing, staying for 5 months while as totally legal, and was detained for 7 hours, interviewed, interrogated, blah blah blahed.... and only by the skin of my teeth allowed in. To this day, a former UK visa holder and current married to a Green Card, I *STILL* get problems at entry gates when I go into the UK.

It seems to have helped some people on here when they brought evidence with them indicating that they intended to return to the US, like a return ticket, a letter from their job, university enrollment papers, etc.  And don't bring any kind of letters or journals with you, where you may have indicated any marriage plans.  UK immigration officers will let you in only if they're confident that you're not going to illegally overstay.
I visited my British boyfriend/fiancé/now-husband every other month over a one year period.  The longest visit was 2.5 weeks.  None of the immigration officers ever gave me a hard time.