imo its very useful on high levels when the a.i. are much faster in science. my trick is not to go into literature. get the other fast-to-get techs first(esp the wheel), while buiding a palace on a city other than the capital. then built a few chariots or fast moving units to look for other civ. at the point when the palace is about to complete, buy literature over from the civ who got it, and immediately trade to others for cash while u switch production to great library. when they start building it a few turns, u already completed it. try to get to know as many civs as possible before completion. u will get more techs. condition is that if 2 or more civs got the tech then u get for free. so the more civs u encounter the higher chances any 2 had develope a same tech and u get it. i got about 12-14 techs for free when i built th great library(i met 3 civs) and hopped right into the middle ages. started my trading session then. got monarchy too so i switch govt. immediately and started building hanging gardens.