From
http://blog.bitinstant.com/"Cash Deposits are currently down on BitInstant as we make steps to transition to our new website.
We apologize for any inconvenience that this may have caused and are working as quickly as possible to reenable this feature.
People have expressed concern that this benefits BitInstant in some way. On the contrary, BitInstant relies on customer transactions, so downtime only hurts us and we are therefore working as quickly as possible to reengage cash deposits.
We will strive to provide future notice for similar situations as they arise in the future to help you better plan your Bitcoin purchases. We apologize for the inconvenience and will post a notice as soon as we're up and running with cash deposits.
Also, stay tuned for an introduction to our new website and its great features! We think it will be worth the wait and appreciate your patience!"