My desktop gets me about 4.4 shares per minute pulling ~250w from the wall(it is not a dedicated mining rig, it has other parts that pull more power idle than would be necessary on a dedicated miner - and I have a few other services running that use a bit of cpu here and there). Electricity is about $0.075 per additional kWh here.
Currently, each share gets me .000029597456 btc through ars.
(250w * 24hrs = 6 kWh) * $0.075/hr = $0.45 cost if that machine runs mining for a full day.
4.4 shares per min * 60 * 24 = 6336 shares per day = 6336 * .000029597456 = .1875 btc a day.
Current mtgox exchange rate puts that at $0.77 per day.
So, $0.32 a day profit. Woo.
Sure was a lot more profitable last week!
A dedicated miner would involve adding 3 more cards, getting a cheaper processor, and downclocking the system RAM(and using a whole lot less RAM), and is much more profitable vs the wattage cost.
But to me it's helpful to know that the computer I use primarily for gaming is also more profitable to have hashing in its free time instead of doing nothing but running servers. Though I don't actually sell btc at this point, I hoard them and also donate them to free services I use like minecraft SMP servers. They're worth more to me than what people are willing to pay for them on mtgox right now.
As an aside - the more merged mining gets used, the higher the difficulty namecoins will have, but is there actually much demand for namecoins for their intended purpose?