I've been thinking the exact same thing lately - what is okay for weddings?!
I'm invited to one and so far I'm thinking bright not dark colours and not short, especially if it's an invite to the service rather than just the evening thing, so I'd be with you on your original instinct. I wouldn't have any bit of my thigh on show in a church, you know? I guess if you're only going to the evening food-and-a-boogie do you can go shorter.
Huge flower patterns seem to be in at the moment, but I always feel drowned by patterns because I'm small and pale so I tend to avoid them.