1-3:
For that level of anonymity you need to connect through TOR, which will be possible with version 0.2, which is only a few weeks away. I'll post TOR instructions at that time.
4:
Version 0.1.5: backup the whole %appdata%\Bitcoin directory.
Version 0.2: you can backup just wallet.dat.
5:
Nope. The whole design is all about preventing that from working.
6:
Those coins can never be recovered, and the total circulation is less. Since the effective circulation is reduced, all the remaining coins are worth slightly more. It's the opposite of when a government prints money and the value of existing money goes down.
7:
It's currently 29,296 blocks. The circulation is the number of blocks times 50, so the current circulation is 1,464,800 bc.
If you only have 24k blocks, it must not have finished the initial block download. Exit bitcoin and start it again. Version 0.2 is better/faster at the initial block download.
8:
Typically a few hundred right now. It's easy now but it'll get harder as the network grows.
9:
Good question, it's TCP. The website needs to be updated to say TCP port 8333.
The port forwarding is so other nodes can connect to you, so it helps you stay connected because you are able to be connected with more nodes. You also need it to receive payments by IP address.
10:
No, the other nodes won't accept that.
Being open source means anyone can independently review the code. If it was closed source, nobody could verify the security. I think it's essential for a program of this nature to be open source.
11:
Slower machines produce fewer coins. It's proportional to CPU speed.
12:
There are more coming.
13:
It uses a transactional database called Berkeley DB. It will not lose data in a system crash. Transactions are written to the database immediately when they're received.
14:
For now, you can just multiply the total blocks by 50. The Bitcoin network has been running for almost a year now. The design and coding started in 2007.