As for keeping a wet edge: that's critical when using oil-based paints. Not an issue with quality latex paints.
Another hint: mix all the gallons together before starting. There will be shade differences between gallons of the same color and mixing together eliminates this.
Also, as others suggested and as th Hometime page recommends, you should not "cut" the entire room at one time, but instead just do manageable protions first so that the paint does not dry before you roll over it.