I had one last year, before the recommended age of 45, due to severe anemia. The worst part about it was the cost, because I wasn't old enough for it to be considered screening.
I found the prep to be not so bad, but I had one that seems very different from most- I had to drink double doses of Milk of Magnesia every four hours (I think) along with double doses of Dulcolax pills. Followed each round of meds with at least 16 oz of water. It was very easy to get down and I was pleasantly surprised with the whole process- I never had cramping or nausea. I was pretty sick from the anemia at the time, though, so I wasn't eating a lot, anyway, and did fine with the clears and then NPO. I stocked up on Gatorade and even bought myself ginger ale, and ended up not touching it, only having water and seltzer and some really not great tasting chicken broth.
They found absolutely nothing- no polyps, no GI bleeding, nothing, so I don't need to do it again for ten years. I recovered fine, with no issues, unlike my endoscopy I'd had a few months earlier. That one left me with a lot of soreness from some mild stretching they did, and I had a hard time eating for a good week or so.