Major performance problems with Selectable

Major performance problems with Selectable

Selectable seems to work fine only as long as there aren't many elements to be selectable. 
With 50 elements performance is terrible, with more (I needed ~500) $('#selectables').selectable() really takes it's time - on a fairly decent hardware Chrome 4.0 takes over 30 seconds and Firefox 3.6 over a minute (but tends to crash).

Any ideas?