Swedens National Day has actually not been celebrated too much through the years in Sweden, except as a general flag day. Although in recent years we have begun to celebrate it a bit more. Like in this video I found on YouTube:
It is a recording of our local National Day celebration in Wämöparken here in Karlskrona, Sweden. It also has English subtitles to our national anthem which is sung in the video.
Originally June 6th became significant because it was on this date in 1523 Gustav Vasa was elected King of Sweden. The 1809 system of government was also written on June 6th. However it was not until 1983 it became Swedens National Day and not until 2005 it became a public holiday in Sweden.