Bing announced improvements to Bing Webmaster Tools where they have added percent changes for metrics on the dashboard.
You can now see percent increases or decreases for Clicks from search, Appeared in search, Pages crawled, Crawl errors and Pages indexed. Here is a screen shot:

The way it works is that it will take the date range you specified, plot that data in the current period data and then look at the same time frame in the period before. For example, if you look at the past 30 days of data, it will compare that data to the 30 day period before that.
Couple technical notes:
(1) With the pages indexed, Bing will show you the percentage change between the last day of the selected period and the last day of the prior period.
(2) Bing's Webmaster Tools data goes as far back as 6 months, so you can compare 30 days, one day, or even 3 months of data.
Finally, Google introduced this feature around October 5, 2010.
Forum discussion at Google+.

Comments:
Praveen Sharma
08/24/2012 12:58 pm
Why it's showing positive green signal for increase in number of CRAWL ERRORS?
Praveen Sharma
08/24/2012 03:31 pm
Can anyone please answer... anyone?? Barry?? Or did I asked something useless? :)
Barry Schwartz
08/24/2012 03:33 pm
Green means higher not necessarily better.
Praveen Sharma
08/24/2012 03:50 pm
but don't u think it should be in red color as for other fields.
Nora
08/24/2012 08:15 pm
i think the same! that's wrong!
Alexander Hemedinger
11/21/2012 06:52 pm
Honestly, does it matter? Let's all admit Google still dominates and all your information should be on Google.