Usability 
Peter Cashmore's Mashable! is a high-traffic news blog covering social networking, web 2.0 and mobile.
I suspect the site's name comes from "Mashup" - combing two (or more) web services to create a new site or service - think of TwitterVision which combines Ttwitter feeds with the Google Maps API to show Twitter updates as text bubbles on a world map. Mashable does cover mashups, especially ones involving popular social networks. But Mashable is a lot more than mashups, with 20 or more news items a day, a MarketPlace section for job postings and Web 2.0 related services for sale or wanted and a page listing invites to startups in closed beta. There's also a daily podcast, usually with the founder or ceo of a hot startup. A popular feature of Mashable is Mashcodes a repository of free MySpace themes, games and plugins. And Mashable itself is a social network, with personal profiles, photo page friends, status updates and messaging.
On July 1oth, Mashable launched a mobile edition at m.mashable.com Unsurprisingly it's a mashup, using MoFuse to generate a mobile version of from RSS feeds of the Mashable's News, MarketPlace and Invites sections. MoFuse is used by a number of sites including ReadBurner and MobileActive (review). It's also one of the services I reviewed in 4 Easy Ways to Make your Blog Mobile Friendly. Since I wrote that piece, MoFuse has added a nicely formatted iPhone version. Another recent enhancement is image resizing, where images are reformatted to a maximum size equal to the screen width. That should make MoFuse pages compatible with more phones, but I'd like to see MoFuse implement page splitting too. As it is, the page delivered to mobile can still be quite large, one of the news items on Mashable today contains 17 KB of text plus 41 KB of images. That's no problem for any Smartphone and many feature phones but too big to display completely on something like a RAZR V3. The W3C and dotMobi generally suggest a maximum of 20 KB text (10 KB markup plus another 10 KB of images) for pages intended to work on any phone.
Mobile Mashable is a subset of the full site but a fairly complete one, offering the full content of the news, marketplace and invites sections. If you want to get to the full site and your browser can handle it, Mashable doesn't force mobile browsers to the mobile version, although if you use a PC browser to visit m.mashable.com, MoFuse displays the content in a mobile widget.