I usually dont research burrow, but i have found that doing a 2-hatch main --> pool build and massing lings with burrow and ling speed early can be quite effective. If u manage to get into his base u can start killing things, burrow when his units arrive and then send in more lings (keep pumping and rally to his base)
Works best vs terran, since zerg has overlords and u have to make a pool before hatch vs toss.