Better bar and tooltip state indication, new Domain mozRank feature, new Show other domains on this IP feature, rankings for HTTPS, left-click to refresh ranking, new Alexa search keywords feature, hide canonical button, miscellaneous fixes.
Canonical link detection with 'C' icon in location bar (!), character counts in Meta Tags, Firefox 3.5 support, private browsing integration, backward links engines revision, improved nofollow highlighting, and bugs fixed.
mozRank from SEOMoz's Linkscape added! Also new Private Mode to only fetch rankings on request, better use of Yahoo's SiteExplorer for backward link checks, and bugs fixed with loading tabs in the background.
Compete.com added! Compete ranking for the current domain now appears in a new bar alongside PageRank and Alexa Rank, with estimated visitors in the menu (can be disabled if not desired). Alexa queries improved to ensure inclusion into Alexa's toolbar users panel.
Firefox 2.0b2 compatibility, the Keyword Density Analyser is more similar to search engine behaviour, DMOZ categories (off Alexa Categories menu), customisable WHOIS source in Options menu, removed anonymization (which was breaking functionality), other small fixes.
Show backward links expanded (Thanks to Todd "Oilman" Friesen!), new link report showing internal and external link counts, Google Trends included, more PageRank fetch tweaks, Firefox 2.0 alpha supported, support for highlighting nofollow links from a meta tag, minor tweaks.