Having tried Litecoin CPU mining out of curiosity the other day, I'd not consider it worthwhile. My 2.0GHz i7 MBP was getting around 4 khash/sec (and running at 99C, so I bottled out). I then tried it on an otherwise pretty idle server, which got a steady 2.0 khash/sec.
Feeling smug that I'd be using spare, paid-for server cycles to make money, I looked up some expected earnings. (Warning: I'm an LTC noob, so may have plugged in bad assumptions), but even at 4khash/sec, I was looking at less than $3 a year
I'd like to be proven wrong on this, of course. However, talking to a couple of people on IRC (hardly guaranteed 100% reliable info, but good enough for me) it seems that even LTC has moved to GPU mining being a lot more realistic than CPU mining)
My understanding is that you need essentially free electricity to make it worthwhile.
Also, Bitcoin is wasteful. People are using an incredible amount of energy unnecessarily. It's a pretty selfish thing to do. This is a flaw in the system's design. I'm not sure other coins are much better in this regard.
The ASIC revolution has turned the tide of energy wastefulness of Bitcoin, and continues to do so. What formerly required a motherboard, connected to a 350w PSU, and a high-powered video card that would (ok I don't know how much of the PSU's amps it actually drained), can now be dwarfed by a 40w or 80w draw. There is almost no point in running a GPU farm today, and around March, if the BTC price is stable until then, it will make more sense to buy BTC on the market than to run these machines. But today it's profitable.
Think of it this way: once all of the coins are minted, the only thing left to protect with all of that hashpower will be the tx fees. If people don't want to pay the fees, then the miners won't get paid, fewer people will be willing to hash, the transaction volume may even have to go way down, and no, you don't need free electricity in order to make it worthwhile.
I have two 5GH/s BFL Jalapenos and yes, they're only making about 0.2BTC or $200/mo at current BTC prices, but they add about $10/mo to my electricity cost in total. That means it even pays for my high speed internet connection, for the time being. I don't know if I'd recommend it to a newcomer, due to the difficulty of actually getting that kind of hardware (I waited 8mo)
But
Think about how many "web sites" I'd have to "host" before I could get that kind of reliable return from running a server computer in my house 24/7. And as a side benefit, I get to use the computer to provide network services (for a small profit, without sucking any... err having any customers to deal with.)
You might want to look into mining litecoin (LTC), which might still be profitable and whose mining is CPU-based.