It means that the results both in PPC and natural listings will be the same in Bing and Yahoo! search engines. This is great news for pay per click advertisers! It means that you will only need to submit the campaigns on one of the engines for it to appear on both. Personally I would use Bing. Bing have a PPC desktop tool that integrates nicely with Windows packages (being a Microsoft product that should be expected).
Will this change the way people search? At PaulSearch we doubt it to be honest. It was more a marriage of convenience as both companies knew that on their own they would struggle against Google. It's better to pool resources and systems to get the best of both worlds and minimise risk.
Bing does have the added advantage of being a Microsoft product, and with nearly all computers having Windows, they are at a distinct advantage. Realistically though people don't "Bing it" they "Google it". Mobile is also the fastest growing way to access the internet. More Android phones are being sold than ever before. Who developed and owns the Android system? Yup you guessed it, it's Google! If I worked at Google I wouldn't be worried about my job anytime soon. At www.paulsearch.co.uk we aim to give our PPC clients the widest possible reach which means if their pay per click budgets allow, we get our clients in the Yahoo! and Bing lists too. The PPC traffic levels aren't massive, but we've found that the CPA is often a lot lower than that of Google, though there aren't as many sales.