Capsule summary: It is a pain in the ass to place SDBs exactly where you want them and then keep them there.
The suggestion about snap-to-grid for SDBs has already been made elsewhere, but it bears repeating. If I'm placing a bunch of SDBs together, it's a royal pain to align them exactly. If I place an SDB overlapping one edge of any already-placed SDB, the second should snap edge-to-edge to the first and align with it horizontally or vertically. This would make it very easy to create even horizontal or vertical rows or grids. Staggered rows could be made equally easily by creating a horizontal or vertical row, then dragging a new SDB to overlap any two adjacent SDBs in the row by at least a quarter of their width, and it should then snap to their common edge but maintain its staggered alignment. If it's off by less than a quarter width, snap should assume that you intended a regular grid.
Arguably, wall cabinets should snap edge-to-edge the same way. The behavior could perhaps be made a preference setting that you can toggle on and off - "Snap-align SDBs", "Snap-align wall cabinets".
The other thing SDBs really need? Lock in place. Once I've placed an SDB I should be able to move or remove it only in decoration mode. Right now, the interface is inconsistent — the default action for dragging something to the SDB is to put it in the SDB, but any time you forget and try to drag something out of the SDB, you move the SDB instead. The default action — at least for any SDB that contains anything, and for consistency, always — when you click on the SDB and drag should be to remove, or try to remove, contents from it. Clicking and dragging on an empty SDB (again, to be consistent; think Principle of Least Astonishment here) should not move the SDB; it should result in a "You need to be in Decorate mode to move this" message.