Looking at my 2012 garden calendar, by this date last year I had planted radishes, raddichio and spinach in my community garden. The crocus, early daffodils, forsythia and cherry leaves were sprouting in my backyard.    While its not to soon for spring, a post today (March 22) on the MN Master Gardener Listserve, reminds us we can be planting vegetables, even with the foot of snow on the ground:

"I've cold-sown all kinds of seeds in many types of containers 
in the last 7'ish years.  I've gotten the best results from:   
1. Seeds of perennials , especially natives (Stands to reason, 
eh?)  

2. Seeds of self-seeding annuals, including tomatoes (Again, 
this makes perfect sense) 
3.  Seeds of cold-hardy annuals like kale, lettuce, 
snapdragon, pansies, broccoli, etc. While a gardener can 
try cold sowing with any seed, in my experience the lowest
 germination rates come from the least cold-tolerant plants,
e.g., peppers.  

As for timing, I am doing my cold-sowing this week.  

While I've done it earlier in the season, I've found no  
advantage in doing so and maybe a slight reduction in 
germination rates in the more cold-sensitive plants.  

When is it too late to cold-sow?  When you can sow seed
directly into your garden! For cold-tolerant seed, that  
means as soon as the soil is workable.  For heat-loving seed,
that means when the soil has warmed to ~60 degrees (F) and
the danger of frost has passed.    

The beauty of cold-sowing
is that the seedlings emerge and grow in concert with Mother
Nature.  Only "she" decides when the seed will germinate and
how fast the seedlings should grow.  And when the time comes
to transplant the seedlings into the garden, they experience
no temp-related transplant shock.  (Sue Schiess Hennepin County
Master Gardener)"

Also don’t forget Terry Yockey’s great link on Winter Sowing.