The points at which I divide up the year seem to be:

• the cluster of anniversaries and commemorations at the February/March boundary
  
• Easter
  
• the first day of Summer (defined by when I stop wearing a sweatshirt outdoors)
  
• the cluster of anniversaries and commemorations at the August/September boundary
  
• November 5th
  
• Christmas/New Year

…so towards the end of February I'll leave my "new year" mindset and instead start thinking about impending birthdays and departed friends.

All the events at the February/March boundary are fairly personal to me, though, so I wouldn't expect my poll response to generalise well.