What software do bitcoin users typically use?

I just got started and am trying bitcoin-qt, but it seems pretty limited. E.g. if I'd buy one of those physical plastic bitcoins with a hash code on it, it seems bitcoin-qt only allows importing it with the importprivkey command which it calls experimental, and does not at all allow you to transfer it from there to a safer address (after allt he one who sold you the plastic coin also knows the private key).

So what software is useful for bitcoins?

Thanks!

If I would keep this address on it, then if someone would send money to it, what would happen? I'm assuming (because it's an example) that hundreds of people have added this. So if it receives money, which person does it go to?

If I add multiple "receive" addresses to my wallet, and each of them receives some coins. If I then make a payment: why can't I choose which address I pay with? How are coins of different addresses combined into one wallet? How can the system know how much coins I have if there is no ID associated with it?

Thanks.

Hello,

I installed bitcoin-qt on my Linux and got a wallet.

For testing purposes, I tried adding the public example of a private key given here:

https://en.bitcoin.it/wiki/Private_key

To my wallet, by using the following command in the console of bitcoin-qt:

importprivkey 5Kb8kLf9zgWQnogidDA76MzPL6TsZZY36hWXMssSzNydYXYB9KF "test"

However, how can I remove it now? I think lots of people have added this one, and I have no clue what it means, I don't want it messing up my wallet.

Thanks.