My office is completely paperless.
Here is what I scan: EKG, lab, spirometry, Xray/CT reports, consult notes, insurance cards.
Here is what I shred without scanning: ER records, hospital records (except D/C summary), home health and nursing home communication, faxes from pharmacy for prescription refills, applications for wheel chairs, O2 or diabetic supplies, PT records
Previous records - I go through them and select those I would want to keep and scan them, and throw away the rest. From what I learn on HIPPA seminars, I am only obligated to keep and release upon request those records generated by myself. I don't have to keep or release records received from patients' previous physicians.
