If you are experiencing poor performance/responsiveness whilst editing features in ArcGIS v10 this can in many cases be remedied by turning off the new snapping tools, which are on as default in v10. This is especially true if the mxd contains a lot of vector layers that are stored on remote servers because ArcGIS appears to query the layers each time you move the mouse to determine the snapping information. The snapping can be turned back on if it is needed, but you can also set the snapping to the ‘classic’ v9.3 mode as well.
To turn the snapping off you need to first turn on the Snapping toolbar, you can then use the Snapping menu and un-tick the ‘use snapping’ option.
To revert to ‘classic snapping’ select ‘Options’ from the Editor menu, on the Editor toolbar, and tick the ‘use classic snapping’ option on the ‘General’ tab.
On this same tab you can also turn off the ‘mini toolbar’ that follows you around whilst editing, which some people find annoying.