Credit Crunch - No Bag Of Glue

I haven't got a bag of glue about whats going on with this credit crunch thing. Can anyone explain it to me in a credit crunch for dummies style? Is it just something we have to go through to stop people getting carried away with the old debt? The Halifax rang me yesterday offering me a quote on my mortgage when it's up for renewal next year. I was told yesterday at work that I could do whatever amount of overtime I liked for the next few weeks. I know the building trade has been hit by it, but isn't that partly because of the shit weather we've had all summer?

Its been all over the news for weeks and I'm still clueless!