I just went to Ljubljana weekend before last. We attempted to go to 2 different gay venues and struck out both times. The K4 Roza bar on Kersnikova was a fail. It seemed to be on some sort of holiday. The area around it was also a bit desolate, so I wasn't so keen on walking there late at night. We also tried to go to a gay bar in the Metelkova complex (near our hostel). We found a youngish crowd at one of the other complexes, but the gay part was closed. We got out of there pretty quickly when we saw a phalanx of Slovenian policemen appear.

Nothing gay to do, but the town is nice. Maybe try Zagreb. I liked it even better.