"Twitter is moving technical operations infrastructure into a new, custom-built data center in the Salt Lake City area. Twitter's user base is growing with over 300,000 people a day signing up for new accounts on an average day. And "having dedicated data centers will give us more capacity to accommodate this growth in users and activity on Twitter," said Jean-Paul Cozzatti.
"Twitter managed data center is designed with multi-homed network solution for greater reliability and capacity. Twitter will have full control over network and systems configuration, with a much larger footprint in a building designed specifically around unique power and cooling needs. The data center will house a mixed-vendor environment for servers running open source OS and applications," explains Cozzatti.
Twitter appears to be on a massive PR offensive to explain to users why they keep going down (or keep shutting off certain features — like the ability to sign-up). Twitter has a post on its main blog, and another by Cozzatti explaining the issues.