Difficulty estimates is never actually accurate. Hashrate can vary due to factors such as ambient temperature, difficulty drop and price rise. The best option is to roughly estimate the worst scenario and see if you can make a profit.

Greenaddress requires you to remember your Mnemonic phrase. If you happen to be travelling and forgot to bring a paper with Mnemonic phrase with you or it isn't stored in your computer, you won't be able to access it until you find it. Greenaddress however, offers more protection against hacking attempts and could lessen the damage. This is however, not necessary for OP as ubuntu have very few viruses around.

In every transaction there's a input. You can spend two wallets in one transaction together. If you accidentally do that, your first address will be tied to the other one and people will know that both of them are controlled by the same owner. Send the change to a mixer for example, [INPUT A] -> [OUTPUT A (The person you want to pay to]) [OUTPUT B(The change) sent to the address you generated using a mixer] the mixer can then send the change to a seperate new address.

OCRs have very low accuracy, they take sometime before it solves the captcha. The ads in the browser could cause computers to slow down and become noticeable. Most faucet uses either recaptcha or solvemedia which is close to impossible to solve using OCRs right now. Think about it, if owners knows their captcha can be solve by OCR s, they would likely to change it as repeated viewing would yield less profits.

It happens with every wallet if fees aren't high enough. Transactions will drop out of mempool if the transaction is in it for a period of time waiting for confirmation. Provided that the client don't rebroadcast it, it will drop out of mempool. If client does rebroadcast it, it will confirm eventually. If you don't mind waiting for longer time and just want to have a free transaction, use a client that rebroadcast automatically or rebroadcast it yourself manually.

Yup correct. It is worth noting that if someone starts a dispute you would not likely win since most of the bank hates Bitcoin a lot. You would not be able to provide a proof of transaction, TXID are not considered as one. If they call their bank and say their credit card is compromised, the bank will chargeback and refundr them.

There are much cheaper option than this. Even with the promo, this can still be expensive to run a Bitcoin. Bitcoin core only needs 1GB of ram a good CPU and at least 40gb of disk space. Look at lowendbox for even cheaper solutions.
I don't get you. The website you provided is a list to the network nodes.

Mining game is really out for everyone even if you invest in ASICs. There are huge farms using ASICs to mine Bitcoin. Even with new hardwares, it may become obsolete even before you ROI. Alt coins are relatively volatile so it wouldn't be a good choice too.

It is currently a captcha service provided by Google(http://www.google.com/recaptcha/intro/) it was originally developed by another team before acquired by Google. Google use it to digitize books and for Google street view to determine location.

AFAIK, no automated bot can solve recaptcha at all. If bots are detected, they will just increase the difficulty. Even if OCRs are created, the accuracy will be very low. Most of them are just human captcha solving services. Solvemedia involves the user to click on the screen which can be abit complicated.

Solvemedia does allow users to earn by using their captcha solving plugin. If you integrate it, it may be a side income. Like pooya said, earning varies due to the location and quality of the visitors. Some advertisers don't pay for visitors from certain country or just pay less.

Review the code and build it yourself then. Why would you say it's of questionable quality and security? It has been verified by lots of people and the lead developer of Bitcoin. It would obviously be a good choice to use 0.9.3 as it is the most stable currently. You would just be wasting your time trying to make changes.

Since newbies would likely not have much knowledge in Bitcoin, they are unable to post constructively on the forum. To truly understand Bitcoin, one must try to send or receive Bitcoin. There's where the faucet comes in.

Greenaddress is pretty safe. Even though it is online, they only keep one of the key to authorize the payment. They need the other key to steal your funds. Even if they close down, you can still recover the BTC you kept there using the nlocktime function.

Unless you are a developer, want to help the network or just want to use the features in Bitcoin Core, a lightweight client would do the job of sending and receiving Bitcoin just fine. Make sure that the lightweight client that you are going to use is opensourced though.

Click the help menu and the debug window. If there is at least one incoming connection, you are running a full node. If not, you have to open TCP 8333.

There was a dicussion about the dropping of the amount of nodes. If there are no nodes, there will be no blockchain and no mempool which is the backbone of Bitcoin.
Bitcoin will die, nodes form the backbone of Bitcoin, having a copy of the blockchain and relaying transaction. Without it, no one will be able to receive, send or mine coins. The probability of this happening is pretty low but running more nodes is better for decentralization.
Yes, you don't have to do anything other than opening ports. You should see more than 8 connections after sometime at the lower right.
No, you have to open ports and more specifically, run Bitcoin Core and download the full chain.

Successful 27 euros transaction completed. A small delay but Cryptology was polite overall. Smooth transaction and would transact again in the near future. Thanks.

Bitcoin node is basically a Bitcoin core setup that allows the relaying of transactions and allow clients to connect to you to download blocks. This strengthens the Bitcoin infrastructure and enables people running Bitcoin client near you to download blocks faster. It is possible to run on any PC that has a ram of at least 1GB ,at least 40GB of disk space and internet connection. To allow clients to connect to you, open port TCP 8333. The network needs stable nodes with high uptime and speed rather than computers that shuts down often as other clients would have to find another node when you shut it down.

512mb would be the bare minimum to run Bitcoind. To run it with some connections, try using 1GB of ram. It is not possible to upgrade ram on this version of raspberry pi however. Do note that SDcard's lifespan will be reduced under heavy load of read and writes.