This can log every keystroke, which will record everything you do on your phone, and it can transmit the information back to Carrier IQ.
It's not clear whether this is happening in the UK or the rest of Europe and nobody has alleged that Google itself approves of this. There is a video outlining the issue on YouTube - search for researcher Trevor Eckhart and Carrier IQ, which demonstrates what he says is Carrier IQ logging keystrokes and recording texts from his HTC phone - this just happens to be his phone, he stresses it's also on Blackberrys and Nokias.
Why do it?
As already stated, it's not known whether this is happening in the UK or anywhere in Europe - if so it would be illegal because of data protection laws. But legalities and regions aside: why would anyone want to do this? There are two possible reasons if it's genuinely happening.
One is a little sinister - they want your information because of its own value. Whether this is because of watching for terrorism, crime and other similar activity or because a marketing departments want to know where you're going on the Internet, whether you're ordering anything through your apps, and soforth, is open to conjecture.
If they'd declare what they're doing with this information, if the reports that it's being collected are accurate, people might even sign up to allowing it. Would you? Let us know in the comments.