The tech space has seen a lot of hires and fires lately, and three big names in cloud, virtualization and social media just joined the club.  The first one is Nirvanix, an enterprise cloud storage company which just hired a new VP. Karen Sigman joines the firm from QLogic and has served at Hitachi Data Systems, DataDomain, and IBM. The new Vice President of OEM and Alliances will report directly to Scott Genereux, president and CEO of Nirvanix. “Nirvanix said Sigman will be responsible for both partner relationships, as well as OEM and strategic alliances in the enterprise storage market.”

Twitter’s expanding its executive roles as well, plucking an industry vet from rival Facebook. Former Facebook corporate development executive Mike Brown will serve in a similar role at Twitter, though he’s bringing a bit of drama along with him.  Brown was dismissed from Facebook for buying company stock on secondary markets, which is against the social network’s internal trade policies.  Now, he will report to Kevin Thau, VP of Business Development. The hiring, as All Things D’s Liz Gannes highlights, is likely an indicator of an up and coming acquisition string by Twitter, which has historically focused on mostly small start-up acquisitions to grow both technology and reach..

Over at the user virtualization front, AppSense hired former desktop CTO at Citrix Harry Labana. Laban, who recently joined Atlantis Computing’s Advisory Board, has served an extended period as the head of Citrix’s flagship business, and brings a lot of experience to the virtualization vendor.

A great deal of cloud companies have made changes to their executive staff over the past few months, and among them is QLogic. Jean Hu is now Senior Vice President and Chief Financial Officer at QLogic, and brings 18 years in strategic corporate development.