Credit Crunch: How big is a Billion?

During the recent financial turmoil the numbers being thrown around by the UK and US governments are making large numbers seem like pocket money. Every week it seems like some bank or insurance company is being bailed out to the tune of a few billion pounds or dollars. The thing is, I'm slightly confused about how big a billion really is. My confusion is that historically I think the US and UK definition of a billion were different:

US Billion = 1,000,000,000, i.e. one thousand million

UK Billion = 1,000,000,000,000, i.e. one million, million

I've been assuming that when some UK bank get 30 billion pounds, they're getting 30 thousand million pounds but lately BBC News have started showing actual figures in their headlines and occasionally I see figures like:

£1,200,000,000,000

Surely this can't be the money given to a bank? It's more than the UK GDP isn't it?

With all these large numbers, it's hard to put into context how much money is actually involved. Another recent trend I've noticed on news programs is to show two stories back to back with the first involving a credit crunch fantasy bailout figure and the second a real world financial figure. For example, yesterday there was a story about Quantitiave Easing (a technical term much more aptly described on Question Time by Shirley Williams as Financial Laxative) involving a figure of £150 billion. The next story told how £140,000 had been allocated to fix potholes in all the roads in the county of Shropshire. To contrast these figures:

£150 billion = enough to fix all the potholes in Shropshire for the next 1,000,000 years

or

£150 billion = enough to fix all the potholes in the UK for over 10,000 years

Where is all this money is coming from? And who does it get paid back to?