If I accept a PhD offer but change my mind about attending, do I have an obligation to attend for some number of years before dropping out? I know there's alot of questions on S.E. about dropping out of graduate school after having started.  My position is similar, but also different:

I was accepted into a prestigious university's program for a PhD in Computer Science earlier this year.  I am expecting to be fully funded for up to 5 years, the school and program are great and well known, etc.

This summer I have been working at this same school as a Research Associate, doing very similar work to the kind of work I understand that a PhD student would be doing in order to work towards their completion of their Thesis and I've come to realize several things:


Upon class signups I realized that I didn't have a particular yearning to take any of the graduate school's offered courses.  I've come to a late realization that I'm not looking forward to any future course work.
Having been working 60+ hour weeks since early May, I've come to the conclusion that I'm not capable/willing to work this many hours.  I would like a life outside of my work/schooling.
The geographic area in which the school is in (and by extension, I am living in) is not one I am used to.  I am finding it extremely difficult to adjust to these new living conditions (Large city, deep south, etc).
This is exacerbated by my perception of the fact that my graduate school is highly composed of work-oriented and often culturally different individuals that I am finding it extremely hard to relate to.  I'm discovering a lack of anyone willing to "hang out" outside of lab or classes.
Personal and family issues are calling me home most weekends, and the school is a bit further from family than I'd like.


That being said, I think all indications point towards me dropping out of the program as soon as my work contract is finished (just before the start of fall classes).  However, I would like to do this as gracefully as possible without burning any bridges, but am unsure of a few things.  


Due to the April 15th resolution, am I obligated to spend any amount of time at this university as a graduate student? (I'm technically employed now, not a grad student). If so, how long?
If above obligation is not present, should I try and remain to attend classes for an amount of time before dropping out to make an effort for the graduate school?  I'm fairly certain at this point nothing short of a miracle change in many factors would be enough to change my mind about wanting to stay for a 3-5 year period.
If I choose to leave in either case, what is the best way to professionally explain the situation?  Who should I explain it to?  My graduate school does not assign advisors until the end of the first year, so there isn't a sole advisor to ask.
The April 15 resolution is a commitment that you won't accept another PhD offer without the OK of the school whose offer you accepted: 


  However, an acceptance given or left in force after April 15 commits the student not to accept another offer without first obtaining a written release from the institution to which a commitment has been made. 


and also a commitment not to accept an offer you don't expect to honor:


  Acceptance of an offer of financial support* (such as a graduate scholarship, fellowship, traineeship, or assistantship) for the
  next academic year by a prospective or enrolled graduate student completes an agreement that both student and graduate
  school expect to honor. 


It doesn't obligate you to go to grad school if you decided you don't want to, after all. 

If you are really sure you don't want to do a PhD, the department will be much happier if you don't start (rather than starting and dropping out), so that they can offer your spot to someone else. In the first part of a PhD, the department is investing (time, money, teaching and supervision) in you with an expectation of future returns. You're not doing them any favors by letting them invest those resources in you when you don't plan to really use them.

You can politely inform the person responsible for the program (e.g. director of graduate studies) that you don't plan to attend after all.