As others have mentioned, a ketogenic diet on the long term isn't good, which is why I cycle.
This is important: depending on your body type, it will take anywhere from <50g to <25g for your body to stay in ketosis. Any more than that, and it'll be kicked out of it. This ties into the carb cycling thing I mentioned earlier, where you do one month @ 20-30g and one month @ 70g. Because you're constantly changing the metabolic rate in which your body breaks down food, there will be no permanent change and thus when you are in the 20-30g ketogenic pattern, it will be just as effective at dropping weight off you as it was when you first started. And providing you don't eat pure shit when you're on the 70g cycle, the weight will stay off of you.
Of course I'd never recommend staying under 30g of carbohydrates per day for anything more than a month or two, at best. But I think it's important you have these facts. If you cycle your carbohydrates, no damage will be done to your mind, your body, anything, since the only permanent change that will happen is the fact that you'll lose weight.
With regard to what Carbon Maestro said, if you want to look your best for a certain day, you have to deplete your body of carbs for about four/five days. On the fifth/sixth day, eat a mixture of simple and complex carbs and make sure you get a shit ton of them. This replenishes the glycogen in your muscles and makes you look extremely shredded and tightens up your skin. It does work, but it's not going to be a long term solution, and it will have no effect on you if you're not that built to start with.
Btw: I'm 6"2, 195lbs, 7% body fat.