Some thoughts:
I think that most people need to pay very close attention while dating.
I think a lot of people don't pay very close attention while dating.
I think most of us really need to realize that if we have a long-time very good friend, who has always "been there" for us, who has reservations about our relationship with our future spouse, that we should pay very close attention to what those reservations are and why our very good friend has them. In general, we know who we can trust with having our best interests at heart.
I think people who stay married for a short period of time are one of 2 things: very immature or in a very bad (read: abusive) relationship. If they are very immature, then I would be angry @ for them not trying to work on things. If they are in a very bad relationship, then they need to get out sooner as opposed to later and cut their losses.
Wedding gifts- if it were me quickly ending a marriage, I would try to return something if it was a tangible (ie-microwave) gift, if it was from my side of the family...obviously with the knowledge that this might not be possible due to divorce laws, community property etc. His side....I wouldn't care what happened to their gifts. That would be his problem to deal with. Money...chances are that it is gone.
Explanation. I would think that people close enough to me to be invited to my wedding deserve some kind of explanation. So yes, I would probably compose some sort of note that I could send everyone...not necessarily containing gory details but outlining that while I know it was quick, conditions in the marriage were such that it could not be saved and that I appreciate their love and support as I work through this VERY difficult time. I'd also try and offer some sort of apology,especially if I couldnot return their gift.
I would be going to a lot of therapy to discern my role in the quick demise of the marriage, and to learn the lessons from it that I needed to learn in order to NEVER make the same mistake again.
My next wedding (if there ever was one) would be very quiet and low key.