I have multiple reports of magic missile locking up the wizard's spellcasting, but I can't dupe it. Any ideas?

Decided to fix this in a roundabout way. I converted this spell to a non-spell. Now it's on a global (skill) cooldown which means it can be used while silence. I think this is a great idea since I think Wizards should have more options while silenced.

How does this play in with spell haste? Used to really count on the fact that MM would fire off quickly with loads of spell haste on Zurrain - is it affected by skill haste now?

Not at all. Now it's affected by skill haste. If you have high skill haste, your other skills will be available to cast faster. It's like a normal melee global cooldown.