I took a first (one of the highest in my graduating year too!) in law at UCL, so I express no opinion on other courses. I certainly didn't have to sacrifice my social or extra-curricular life at university - I had a great time with friends and was very involved in various activities at uni. I think organisation and efficient time management is the key.
I do not buy any of the 'I did no work at all but a first just fell on my lap (obviously because I am so incredibly clever)' remarks. You have to put a certain degree of work into your degree. Without the background knowledge, how can you write in the exams? Of course, it is true that some people need to work a lot less than others to obtain the same results. I certainly studied much less than many of friends who got 2.1s, but I did study (while doing a part-time job which I enjoyed very much)!!
I read someone's post about having passion and enthusiasm - I fully agree. I think that is especially true for humanities and social science subjects. If you are not passionate about your subject, you will not be able to express those sparkling insights with clarity under the pressure of your summer exams.
As for those who think that it makes no difference whether you get a first or a 2.1 from a top uni, all I can say is this: you obviously have never enjoyed the pleasure of being headhunted and tempted with very generous signing-on bonuses (£35000 starting pay, £4000 sign-on bonus, £2000 for clothes, 6-month secondment to New York with apartment in Manhattan, etc) by various top international employers. :-)