Previously you were able to submit up to 10 URLs per day and maximum of 50 URLs per month. Bing increased these limits by 1000x and removed the monthly quota.
The announcement. Here is the slide where Fabrice Canel from Bing announced this on stage:
Here is his tweet as well:
How do I access it? Log in to Bing Webmaster Tools and access the the Submit URLs feature in the Configure My Site section.
Here is a screen shot:
Why it matters. Many SEO Companys and webmasters like the ability to submit new or updated URLs to Bing or Google for faster crawling and indexing. Here Bing is allowing you to submit a huge number of URLs per day.