I've actually thought about trying to get some wedding gigs. It would be a fun way to get a little extra income. However, i'm unsure if my D90 would perform sufficiently. I'm concerned about the high ISO capabilities, and that clients would expect rather clean and noise free images.
TQ, A few years ago a good friend of mine who was a professional with fifty years experience doing weddings gave a lecture to a photo club in Florida. Subject of the lecture was "Doing Weddings." It was a one-word lecture. He got up and said, "don't!" And then went on to explain why no amateur should take on a wedding. Another pro photographer friend who had an office down the hall from mine in Colorado Springs once told me what happened in film days when the photo lab screwed up his negatives from a huge wedding held at The Broadmoor hotel. Having to explain the problem to his clients was not conducive to long life and good health.
I did a few weddings in the sixties, hated doing them, and quit doing them. My final pro gig was a debutante coming-out ball at the Peterson AFB officers' club. (You apostrophe folks take note.) I've told this story on LuLa before, but I'll bore the old-timers by telling it again. I went to a dress rehearsal a few days before the ball so I could find out where the debs would stand when they curtsied to the general, and see what the lighting conditions would be. There were about fifty women milling around, and every one of them was independently in charge. Nobody could tell me anything with any real authority. The night of the ball I had to wing it. I had the right stuff with me, it came out all right in the end, and I made a nice chunk of change on the job. But at that point I swore off "professional" work.
Doing a wedding is like walking a high wire without a net. If something screws up there's no going back and doing it again. Both the pro friends I mentioned can tell stories about cameras and lights that failed, and a host of horror stories about some of the people you'll meet, and have to photograph without making them look like gibbering idiots, at the average wedding and reception -- especially if there's booze at the reception, which is normal.
No, your D90 won't even begin to do the job by itself. If you're going to do a wedding you need to shoot with at least two pro-level cameras. One may crap out on you. You also may find, when you pull the card from your single camera, that the pics on the card are scrambled, or failed to record properly. If it hasn't happened to you yet and you keep on shooting, sooner or later it will. And you can be sure that if it happens, it'll surely happen when you're on that high-wire.
Sorry. Couldn't help it. Just had to unload. If you don't believe me, go have a chat with a local pro who does weddings. That kind of pro work is nothing like amateur shooting where you can choose your own times and your own subjects. Fine art work is Heaven. Weddings are Hell. Doing weddings most emphatically is not "a fun way to get a little extra income."