given the difficulty how many hashes on average are needed to find a block?

do you mean that if I bought BTC at 30$ I must keep and wait until the price raise again above 30$ ?
This may be or may be not a good strategy...
In general,  trading strategies that prescribes rules of action based on the price you paid are wrong.
The price you paid is the past and you cannot change it. Trading is a bet on the future.
The only things that counts is your prediction about future prices.
The general strategy for trading is this: start with half of your capital in BTCs and half in dollars.
When you feel like it's time to bet on the increase in price of BTC, move some of the capital from dollars to BTCs, viceversa if you want to bet on the decrease of price.
The amount of capital that you move must be proportional to the estimated probabiliy of increase or decrease of the price.
If you you can't tell what the future will be, keep your capital split equally between BTCs and dollars, that is equivalent to not betting.
How you can predict that future price and the probability of it, is another story....

and then probably facebook will say: "ehi B, where did you buy those FBs?? You are allowed to buy only from us. Your account is closed."
They can do that.

hihihi ogni volta che si parla di kWh nei forum cominciano discussioni infinite

Perché non provate a ragionare con i Joule? E' più facile!

Joule è energia,cioè una quantità.
Joule/h = Joule all' ora, come i km all' ora delle macchine, è una velocità, cioè la velocità con cui si consuma (o si produce) energia quindi una potenza.

1 kWh = 3.6 MJ (MegaJoule)
1 kW = 3,6 MJ/h

Costo dell' energia: 6.6 cent/MJ = 0.24 €/kWh

Beh, io ho guardato la mia bolletta e facendo tutti i conti (veramente complicati...) mi viene un costo totale di 0.24€/kWh...
Questo nella fascia oraria più alta, la differenza con la fascia più economica è minima (sui 2 cent, credo), almeno per me e se non ho sbagliato i conti.

The idea of a master key is very good.
It is already used by programs such passwordmaker (open source) which i use with great satisfaction.
Anyway i think that periodically is necessary to create a new set of keys, that is a new wallet to which transfer all the funds, discarding the old wallet: we can never be sure if a certain wallet is compromised or not.
This operation, in my opinion should be executed before every backup and in case we use a master key we should generate a new one.

Here in Italy, it is a crime to burn or otherwise destroy money, even your own money.
I never have known exactly why. I suppose this law has  never been applied...

Nobody is mining on testnet?
Maybe tesnet bitcoins will have a real value... after all they are really needed for testing purpose

Quando cambi il wallet non c'è bisogno di riscaricare la block chain. Il programma dovrebbe fare un rescan di tutte le transazioni nella block chain per calcolare il saldo del nuovo wallet.
Per la verità non so se il client adesso fa il rescan automaticamente ( quando ho fatto delle prove non lo faceva).
In ogni caso c'è l' opzione -rescan oppure si possono cancellare i file blkindex.dat  blk0001.dat e riavviare il client. (vedi la voce "restore" in https://en.bitcoin.it/wiki/Securing_your_wallet )

Saluti.

Hi
I'm Enzo from Italy.
I have been following the bitcoin project for some time now and I find it very interesting.

Beware of the bubble

So I stumbled upon a bug in bitclient (a minor bug, obviously)
I would like to  point out that there's no need of an high precision calculator: target is a big number but with few significant digits. The maximum target has only 4  significant hex digits (FFFF), I don't know how many there are in the current target but I suppose there's no need for it to have many more.

I don't understand this:

$ curl --url http://***:***@127.0.0.1:8332 -H 'content-type: text/plain;'  --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getwork", "params": [] }'
{"result":{"midstate":"df92c2b8aac64fc5d15a0ff08a8950453ce9e8fb1ecfa39cb8aeaca78bae173a","data":"0000000174dae8b4ae722300d81693b97993f4a57dc7c8151b980d4a00003bfc00000000b79f998 e1df8db02f7d2ba1676e7060a57fa8a5764990629f53173f8b61d8c1f4dde5b591a44b9f2000000 0000000080000000000000000000000000000000000000000000000000000000000000000000000 0000000000080020000","hash1":"0000000000000000000000000000000000000000000000000000000000000000000000800000000 0000000000000000000000000000000000000000000010000","target":"0000000000000000000000000000000000000000000000f2b944000000000000"},"error":null,"id":"curltest"}

$ curl --url http://***.***@127.0.0.1:8332 -H 'content-type: text/plain;'  --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getdifficulty", "params": [] }'
{"result":244139.48158254,"error":null,"id":"curltest"}

$ echo "base=10;ibase=16;scale=8;00000000FFFF0000000000000000000000000000000000000000000000000000 / 00000000000044B9F20000000000000000000000000000000000000000000000" |bc
244112.48777433


Why I get 244112.48777433 instead of 244139.48158254 ?

Enzo