1. The combined Checkbox and Textbox cell (Standard cell with checkbox enabled) is a great thing, but is it possible to change the view, so that the Checkbox in a specific column appears not on the left but on the right side?
Yes, it is possible. At the nearest time we'll publish a sample that shows how to make this column type.
2. Is it possible to use \"user-defined\" .Net controls within a cell?
If you mean embedding - no. But it is possible to use any windows.forms control as dropdown of cell editor. You can see the Grid Stylizing example and try to edit CustomDropdown column cells.