Ok I shot a wedding. Well technically.
I was invited to a very small wedding, of some family friends, and brought my camera along in case they didn't have a photographer. When I got there I only saw someone with a small point and shoot trying to take photos. So I pulled out the K-1 and lowly 28-105 and went to town.
The ceremony itself was in a very very dim setting.. in a gymnasium converted into a church sanctuary (so no windows) with most of the lights turned down.
I wasn't sure of the use of flash at the time so I didn't have one on my camera. Just cranked up the ISO past my normal comfortable zone.
I will say two.. no three.. things about my experience:
1) (If flash is allowed -- ASK ahead of time) Get a TTL flash
and learn how to use it properly.
2) Plan shots ahead
3) You will miss much of the actual ceremony as you will be watching everyone to get photos at the right moment
Just before the wedding ceremony started, another photographer (with a flash) showed up. (doh! on the flash) And no one was complaining. So, in light (no pun intended) of the situation, I let her take most of the photos.
I did sit near the front and on the outside by the aisle. So I got shots of the bride and sort coming up the aisle (the other photog was not positioned in the right spot to get those).
Without the flash though, they are pretty grainy (as to be expected).
This means a lot more time in Post pulling out grain and trying to retain detail... it would have been smarter to just shoot with a flash.
The fast lens would be nice too. But even that won't fix the issue entirely. For much of the ceremony, I was shooting at 28mm and f/3.5 --- f/2.8 is only what a half stop down? I still had to crank the ISO to 6400 and pull up a little in post
Get a flash.