Mashable used to look like an advanced news blog, with static content, now the site is more dynamic, with continuos down the fold loading of posts, a look like Facebook news feed or much more like pinterest, which is indeed (pinterest) like an idol for websites themes who is being followed by many websites all over the world.
[ALT="Mashable"]http://s10.postimage.org/hvjto4z3d/Screen_Shot_2012_12_09_at_1_39_08_PM.png[/ALT]
Also advertisements are not only posted as Google adsense, but also Double click ads are posted like posts thumbnails, which is more attractive and good looking than previous conventional ads.
About the new script, it is believed that Mashable used a blend of these scripts : Ruby on Rails, Backbone JS and Handlebarsare.
After new Digg.com and new Mashable.com, Pinterest seems like a fashion boom on the internet, seems all websites now are trying to provide similar look.