I'm only a first year, but so far this has happened:
Before medical school:
Allergy/Immunology, general surgery, or family med - definitely not OB/GYN
Post-first block of med school:
Rural/3rd world country family med (first block of med school puts you right in your place
)
A few blocks deep:
Allergy/Immunology, General Surgery, Family Med, or Radiology
Winter break:
General surgery Allergy/Immunology, Family Med, or Radiology
Post-GI Block:
Allergy/Immunology, G.I., General Surgery, Family Med, or Radiology
Now (after our first neuro exam):
Neurology, Radiology, General Surgery, Family Med, Allergy/Immunology, or Internal Medicine (only because my interests keep increasing
)