I'm on a MBP Retina w/Mountain Lion and experiences that the "Expand selection to line" (cmd+L) is really slow/laggy when several documents are open/tabbed in ST2. I have 8 tabs in my current window and two other windows minimized with 5 tabs in total. The lag is quite substantial, I can maximum press cmd+L once a second to get the selection executed, whereas with cmd+D my own quickness is the limiting factor.
An obvious fix would be to close as many tabs/windows as possible, preferably working in only one document, but that's not very SL2-ish. Any other solutions?