We actually *just* migrated from Apache to Nginx a few weeks ago (at the same time we migrated to XenForo). Litespeed wasn't even in the running for evaluation for me because I wanted something with SPDY support.
I remember looking at Litespeed a few years ago and it wasn't bad... In fact for some things it was the best option. But it didn't do anything remarkably better, so the cost of the enterprise version was an issue also. Maybe now it does stuff much better, but for *me*, the fact that SPDY protocol support isn't an option at all makes Litespeed not an option at all for me.