I took my 5D2 & 85L to my coworker's wedding and occasionally snapped some images from my seat for my own enjoyment. Now I strategically chose my seats for the ceremony & dinner no doubt but I never stepped on the toes of the 'Hired' or gained attention to create photos outta respect. Besides, the main purpose of going was to have a good time, photography was only secondary.
In the end, all the images were candids that I enjoyed as well as my coworker(the bride). Once I tagged her on FB, all her friends that were at the wedding thought I was the main photog, so after I cleared that up, two parties still booked me to shoot their weddings this year.