one thing you got to be careful with is missing parts ... i.e. if you get a refurbished motherboard it may or may not come with all the cables, faceplate, whatever stuff normally comes with a brand new boxed motherboard. I have extra parts, so missing parts aren't a big concern to me. When it comes to hard drives and processors ... it may arrive still not working, but you can RMA it ... meaning you can send it to the manufacturer of the product and get a replacement. For example, I got a refurbished Samsung sata drive that refused to work for me, so I RMA'd it to Samsung and they sent me another one.
Word of advice ... unless you have a resource to get cabling and such, I'd purchase a new mobo. You may get lucky getting all the stuff that normally comes with a new mobo, as I did one time, but probably not. I got greedy and tried to buy another refurbished mobo and it didnt come with the custom faceplate. Makes it look kind of goofy on the back of my pc, I dont really care though ... no one sees it.
But cd-rom's, hard drives, floppy ... etc ... there really isnt anything extra that comes with them that you would lose. With the processor ... make sure it's a "retail" refurbished ... not a "OEM". Retail means it will come with a heatsink.