I am afraid, that you cannot find any Sopot song festivals this year, but certainly next year 2011 as it is 50 anniversary celebration of these song contex there.
I visited Sopot during last weekend and could see only a huge dig remont on the site of this outdoor theatre located on the forest hill, about 1 km from the centre.
But the new stadion will be very nice, I could also see some advetisment there.
Anyway, Sopot and also Gdynia are great places to visit during summertime: you can get there from Gdansk by local trains.
Regards, Jouni from Finland