[gumby]

How about the "snap to grid" metaphor, same as (e.g.) Omnigraffle, with a way to toggle on a per-drag basis? That's a common Mac metaphor.

Then the grid could be a function of your zooming...no that would be too confusing. The other way: have a "zoomer" for the grid itself.

Hmm, I can see why a program like OG or MSProject in later versons can look so overwhelming!