As Father Bill said, much depends on the desires of those getting married. Some opt for great formality, others for less.

Another factor is whether you are a guest or a member of the wedding party. If you are part of the bride's or groom's "team," there will likely be a sort of "uniform" expected. As a guest, you have a lot more leeway.

At any rate, I would always check with the bride or groom, to make sure I wasn't "out of step" with what the couple wants for their big day.

Andrew