Status Update is built-in to vBulletin 5. Updating status is done on your User Profile page under About tab but it only shows up below your avatar and name on your User Profile page. This modification exposes it a bit more by displaying it in the postbit section of a post in a thread. This will encourage forum members to update their status.

Compatibility: vB 5.x.x

Demo:
See demo and CSS customization here.