The new stuff includes a new mobile client, Mabber Alerts for RSS on your phone and an interactive Helpbot (lots of fun - play Turing tests with it). Mabber opens new windows for everything - the chat client, configuration and buddy list - but many prefer to have their IM in a new browser window like this, since it's more like a desktop IM (Meebo does provide a pop-out window as an option).
But it's the widget that's really interesting, since it could give Mabber the viral boost that's driving Meebo's growth. Alas, I had some issues: after errors stopped me creating an account, I eventually logged in with BugMeNot, only to discover that the widget just wouldn't work. Another issue: why oh why did they use an iFrame? Flash would have ensured compatibility across social networks (particularly MySpace, Piczo, hi5), blogs and anywhere else people wanted to embed these things. An iFrame, however, does not. So, the jury's out on Mabber's updates, and even when the technical issues are fixed, they may have missed out of what made MeeboMe take off. Good job on embracing mobile, but the web side leaves something to be desired.