I filed a bug related to the "snap guides while dragging" behavior: https://bugs.launchpad.net/bugs/181020 Diederik did a great job fixing its behavior, now it is more controllable and does what it should. The problem is that it's not clearly explained what sould it do. In the same bug report Diederik explained why it's not possible to snap to segments atm, so he had to apply the snapping to the points only. Knowing this, the snapping works perfectly. imo, the only thing that should be changed is the checkbox label: "snap guides to points while dragging". As it is disabled by default, people will have to read the label to turn that feature on, so there's no excuses like "people don't read tooltips".
About the other Bulia's proposals... I agree. The snapping options should be unified and simplified to make the easier to understand. The features work great, but the UI is slightly confusing.
Regards, Gez.