Since Zealot seems to be concerned with profit, here's a personal example in favor of mining LTC over BTC right now using the calculator quoted above assuming no cost for electricity and no fees:
GTX 570
BTC:
Hashrate: ~140 MH/s
Coin Per Day: .008 BTC
Profit @ Current Price per day: $0.726
LTC:
Hashrate: 220 kH/s (0.220 MH/s)
Coin Per Day: .613012 LTC
Profit @ Current Price per day: $1.554
As you can see, mining LTC with a GPU is more profitable than BTC (right now at current market prices)
I'm mining on my A10-5800K. I'm getting 85MH/s SHA-256 and 55KH/s Scrypt. So that's $0.44 a day for bitcoin mining and $0.38 for litecoin. So it just depends on your hardware I think. A lot of cards do about an equal amount of MH and KH so in that case litecoin would be worth it.
I've been mining bitcoin and exchanging for litecoin. I think it's a better position to be in. Bitcoin is overvalued and litecoin is undervalued in my opinion.
One thing that I have a problem with litecoin is the mining pools available. They're not as well developed as with bitcoin yet and they're not really clear on some things like whether or not they share transaction fees. I'll personally be staying with bitcoin even if it's 5 or 10% less profitable than litecoin because the litecoin pools are a lot more shady and likely to collapse for now, taking your earnings with them. I wish bitminter would hurry up and start doing litecoins!