How is the bitcoin 21 million cap implemented?

Just to check what would take for that limit to be changed. (not that I want to be changed, quite the opposite). I know the total number of bitcoin reward is halved every 4 years.

So does the verifying nodes check if the number of rewarded bitcoins match the distribution schedule?

Installing Bitcoin-Qt on Ubuntu

I am using Ubuntu 11.10. I have downloaded Bitcoin-Qt, but I don’t think it has installed itself. The instructions say “download and install” the software, but I’m afraid I need instructions that are a little more specific. If you can tell me how to install the software it would be greatly appreciated.

Does IBB make money? Where does its earning come from?

Slightly off topic, but perhaps it is still marginally on topic because it’s about a Bitcoin-oriented business:

IBB is an “Islamic bank, acting according to the Sharia (Islamic law), charging 0% interest on BTC loans”.

Is it a profit-oriented business? A charity? Does it make money? Where do its budget come from? (I saw they’re advertising on the Bitcoin forum today)

I know they issued some GLBSE stocks, that might explain the source of the money – are Muslims effectively “donating” to this bank by purchasing stocks?

Bitcoin as subscription method

I am contemplating designing some minor sites that uses bitcoins, but as far as I can see, a manual action is needed for every payment.

Is it possible to set up a “subscription” system or repeating transactions?

If not, I am planning to design a system where you can replenish your subscription, by simply “filling up” your account and then over time the allocated coins will be depleted.