Just spoke to Linda Scott in the Bioengineering dept. at Caltech. Apparently they're doing something different this year and not extending interview invitations to all of their 'possible admits' due to some problems that occurred last year. If you call her up you can get your application status. She wasn't sure how it was going to work but she did tell me that an interview did not necessarily mean a higher chance of admission.
MIT is also still reviewing applications.