In SC1, there were very tight build orders where you will know exactly when to save larva, save gas, or build Extractors. This has been somewhat lacking in SC2. If you watch even top level Zergs, they will often just try to get 3 bases up, go Ling/Muta/Baneling, but are not very consistent with when the Baneling Nest is built or when upgrades are researched. In my opinion, the ultimate tell when a build is tight is how the gas and larva are saved up when the Spire is done. Again in Starcraft 1, 2 Hatch Mutalisks were extremely deadly because it hits at a specific timing and could be disguised as a 3 Hatch Mutalisks build, messing up the timing of the Terran. I've been looking for that same type of aggressive timing in SC2.
The series between Jinro and Line really showed off Line's very tight build order. He employed extractor tricks at 18 supply to get out 6 lings and a Queen. He had 100 minerals at the exact time he got 100 gas. His timing to get his extra extractors was perfectly aligned with his Lair and Mutalisks timing. All of these maneuvers allowed him to have exactly enough minerals and gas to get 8 Mutalisks at roughly 10 minutes. He did this while being very safe (made more than 30+ lings before Mutalisks) and putting down a 3rd. Of course, there are many builds that can get Mutalisks out faster than this or rush to 3 bases faster, but as both games has shown, this build is a good blend between hyper-aggressive openings and super macro 70 drone builds.
Without further ado, I will detail Line's build order with a link to the VODs at the end.
Line's ZvT "2 Hatch Mutalisks"
10 Extractor Trick
16 Pool
16 Extractor
15 Hatch
6 Lings when pool is done (17/18)
Extractor trick to get queen out
19/18 Overlord
@100 Gas, Ling speed (Roughly 3:51)
23 - Second and 3rd queen
Add lings and drones as needed
28 - 2 Overlords
Put drones back on gas at 36 supply
Get Lair when possible
At 150 Gas after Lair started, Add 3 Extractors (Roughly 5:40)
Make a round of lings to be save (around 24 lings)
Expo to a 3rd at 9:30 (or around 90% Spire completion)
8 Mutalisks at 10:00
http://www.gomtv.net/2011super1/vod/65441
As you can see, this is not a simple BO but it is very beautiful and exact. Since you get Ling speed very early, there is an option to do a Baneling aggression if you see a Terran being super greedy. I've yet to try this build myself on the ladder but I will do so as soon as I get some time tonight.
Enjoy!