I also use Sketchup mostly for creating laser cutting files.
My own experience is that AutoCAD (dxf,dwg) files rarely work well - for example, the segments making up a curve will often all be exported as many small 'closed' curves, such that every small segment is cut individually from one end to the other and back again, and often in seemingly nonsensical order.
For this reason, I tend to use the SVG export plugin that Jim suggested (together with CorelDraw or InkScape if I need to tweak the SVGs) - sounds like a hassle, but I find it can actually be far less labour intensive than trying to 'clean up' an AutoCAD file.
Of course, this will depend on what cutter/laser software you are using - so let us know what your spec's are; if they are the same as what I use here, I'd be happy to share what I've learned over the last year or two.