The speed limits are in Finland defined with “maxspeed” ( http://wiki.openstreetmap.org/wiki/Key:maxspeed). The special thing in Finland is that we have different speed limit in summer (~from April to October) and winter. Those are usually defined with “maxspeed:seasonal:summer” and “maxspeed:seasonal:winter” tags. Sample: http://www.openstreetmap.org/browse/way/61840557/history. There is also few with maxspeed:summer / maxspeed:winter.

I did spend some time and create (bad) map about speed limits in Finland (situation 11.07.2012 / will not update): http://www.latukartta.fi/maxspeed/highway.html. The actual motivation was to make visual speed limits in my area - it’s easier to update stuff when you know what has being done. There is
for : maxspeed=120 define line-color : blue
elsefor : maxspeed=100 define line-color : red
elsefor : maxspeed=80 define line-color : yellow
elsefor : maxspeed=70 define line-color : black
elsefor : maxspeed=60 define line-color : green
elsefor : maxspeed=50 define line-color : purple
elsefor : maxspeed=40 define line-color : black
elsefor : maxspeed=30 define line-color : brown