Zerg Strategy: Stupid mistakes even pros make

I've watched a couple of Day9 dailies and GSL pro games lately, and I was struck by the following mistakes by Zerg players:

• Making a Spine Crawler wall without any Spore Crawlers for detection
• Making Spines to protect against marine drops, but no Spore to kill the medivac, such that the marines can just pick up and fly away again.  Spines also suck against upgraded marines, by the way!
• Poor building placement, and not using buildings to wall off against hellions, for example
• Failing to spread creep in one's main:  for vision, Queen movement, and so that Spores can be placed to ward off drops and air units
• Forgetting to retake Xel'Naga watch towers
• Not building a single Overseer to accompany one's lategame army.
• Attack-moving up a ramp with one's whole army, leaving all the units except one to dance around trying to attack the one cannon at range instead of mowing through the wall.
• Overproducing Hydras.  Seriously - Hydralisks suck for almost everything (other than perhaps defense against a Gateway army by Protoss), and even if they help you defend a push or air attack, they are terrible at counterattacking due to their low speed, and should be considered more of a slightly-more-mobile fixed defense.  I think they are even worse than fixed defenses because of their low hp.
• Moving your Infestors with the same hotkey as the rest of your army.  Nothing gets these expensive, awesome units killed fast than letting them A-move to the front lines and get pulverized without doing a damn thing.

While I don't advocate working on this at the expense of your macro if you haven't hit Diamond yet, if you're going to fix a few last things about your game play, do these too.

Zerg Build Orders You Really Shouldn't Try

I just watched a GSTL match between Zenex and OGS, where the Zerg player, with the match on the line, used a Roach-Hydra based army in a ZvT.

Why is this a bad idea?  Simply put, Terran almost always uses Tanks against Terran, and Roaches die quickly to tanks, and don't even do well against upgraded marines because Roaches are too big to get a good position against the tightly-packed marines before they lose too many of their number.  Worse, Roaches are nice beefy units, but aren't very supply-efficient.  Thus, using Roaches in the later stages of the game is a bad idea.