NX6 holes, things I wish they'd told me from the start:
It's actually a good system this.
When you place a hole you can still use an existing point (right hand icon near top of menu), this is good for putting holes on centres of bosses etc.
Most often though, use the sketch. Click on the "sketch" icon to allow you more control on the sketch orientation.
It's just a sketch with a hole placed for every point you put in the sketch.
Normal lines don't produce any feature, so you can draw rectangles to control 4 holes and other lines to constrain things.
For example, to centre a grid of 4 holes on a block I'll draw a rectangle, put a point on each corner, then draw diagonal lines from the bottom left of the rectangle to the bottom left of the block and likewise at the top right.
Make both extra lines parallel and equal length and with just 2 dimensions you can control the whole grid of holes.
The only downside with the new hole feature is that you can't change tapped holes to simple holes or vice versa afterwards