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To clarify my original comment, when using an Apple Magic Mouse, the scroll to zoom feature is overly sensitive and will fly in/out at the slightest touch. It's an essentially unusable feature with this mouse; hence the request for a key command.

Those are helpful, but really what I'm looking for is more like guides in photoshop:

I had posted a similar feature request over a year ago, but it does't seem like the updated grid functionality has been implemented.