Shacking Up--Living in Sin or Smart Planning?

I've been working on this post for awhile now as I am in the process of apartment hunting with my boyfriend, and it seems that I have quite a few friends who are getting ready to move in with their significant others or recently have done so. Today I posted on my Facebook status-[Ace of Rambles] wants YOUR opinion--Is it considered 'shacking-up' if you're engaged? And does 'shacking-up' even matter these days? The responses came in...and quickly. There were a variety of responses, but mainly fell into these categories-

1. Shacking up is sin.
2. Living together before being getting married is bad idea.
3. Living together before getting married is a good idea, but shouldn't be done for a long period of time.

I can definitely see all three sides (and there are probably more) to the argument. I spent the better part of my childhood witness to my mother living with a man that she wasnt married to, and for the most part to this day I still refer to him as my step-father though his relationship with my mother has dissolved. I personally don't think them choosing to live together before getting married was what caused their relationship to end, but I'd have to ask my mother and him to be totally sure. I have also seen living together prior to being married bring two people closer together, as well as the couple maturing together and individually. I have a friend who was dating someone for 3 years before they lived together. They lived together for a year and she knew that she was not ready yet to make that commitment. They took another year apart and now they're back together and they feel things couldn't be better.

A different friend of mine expressed that her reasoning for not wanting to live with someone prior to marriage is because she likes her own space. I feel that someone who claims to enjoy their personal space so much would be more likely to take a trial run at living together before getting married. What happens when you think you are ready to be married, you get married, and the 2 months after living together you realize that marriage is so NOT in your life plan, and that you value your personal space much more than you realized?

I echo the sentiments of one of the responses on my status--"I believe in trial runs...I don't agree with livin together for years and years before marriage.if that's the case just call it common law and never actually go to the courthouse.but I do believe its necessary for ppl to know how they'll truly interact with each other once they're personal space is taken away. Spendin the night is not gon give u the full effect. Spendin a couple months with each other def will....I use my friend as an ex. She and her bf were together for 2 years and they were thinkin bout marriage...lived together for 6 months and decided they just weren't ready for that step.sometimes u gotta know where he keeps the ketchup...in the cabinet or in the fridge.lol" Many people think that spending the night with your significant other will give you idea of how it will be to live together, but I disagree because when you spend the night you ALWAYS have the option of going home when you want your own space.
I obviously fall into the 3rd category. I believe that living with my boyfriend will be good for us. It is something we've discussed extensively and share they same philosophy. We both agree that moving in together is the next step in our relationship, but more importantly we both know it isn't something we will be doing for an extensive period of time without walking down the aisle. Before we ever started dating he made it VERY clear that the next woman he got into a relationship with would the last.

Our decision to live together was just that our decision. I'm not concerned with whether or not people agree because we are doing what we think is good for US.

What are your thoughts?

-Ace of Rambles