"Great" is not the right word. Right now, a 600KH/s Litecoin miner at 200 watts is mining $0.79 per day after electricity. That's 3 cents per hour. The best altcoins may get you a dollar a day or so. I can probably find more on the ground walking around the mall. Alt coin prices seem to be falling over time, which will only make mining less profitable.

As less efficient GPUs become unprofitable (many are already), you will likely see declining network hash rates among alt coins, killing them off when split blockchains and orphans become unmanageable. Eventually we will probably be left with only a couple (thankfully), and those will be marginally profitable for the more efficient GPUs and those with low electricity costs.