Bing was launched earlier this month by Microsoft. It is an attempt to compete with Google and whilst Google are taking the launch very seriously (Microsoft is rumoured to be spending $100 million on advertising the launch), the consensus for the UK launch is that Microsoft have made a mistake launching it in the UK without all of the features available in the US version.
From a SEO and SEM point of view, like everything, it will be a case of testing. The initial feedback from UK oriented posts that I have read is not very positive. The general view is that Microsoft launched the service prematurely in the UK, however, only testing will tell. On a positive note, there is a view that the way Microsoft have designed the interface causes people to spend more time on the page, which can only be a good thing for advertising revenues.
Check out Bing at discoverbing.co.uk