Things are changing according to globalization and probably more to EU legistlation. I remember the times when the market was run by Swedish sellers but nowadays the area is full of similar Southern Europe sellers having same stuff and same prices and they all are selling from early afternoon (at least) with half price. The prices has been high on the morning, right. Flowers, vegetables, berries and fruits are in the sales list.
The crowds are still there the stairs are common sitting place and I spend there part of my sunny day, but the original feeling has gone, the place is not the same anymore.
Stockholm concert house, Filmstaden Sergel, departmentstore PUB and Hötorgshallen are located in the square.
By the way, watch Madonna's music video "Ray of Light", you can find the square from it (the video is directed by a Swede, Jonas Åkerlund).
This is one of my favorites places in Stockholm. The market here is always full of life, colors, aromas and happy people - and here is the only place where I feel safe haggling. As far as I know, the market is open from 8am to around 6pm and it goes on no matter the weather (unless there's a storm or the like). Some of the things you can buy here are fresh fruit, flowers and clothes (knitwear).
Edit May 2010: if you go around the time they're closing, you can get some deals with the produce they didn't have time to sell. Today I got 2 small boxes of strawberries for 20 SEK (about 2 euros). Very good price considering that the same item costs at least twice more at the supermarket.
Watch out for pickpockets while walking around here.
A square where you can buy fresh fruit and flowers, there is a movie theatre a shopping mall food court, koncert hall and close to sergelgatan (shopping street)
Very popular meeting point with department stores, consert house, movie teather, outdoor/indoor market...