I have been using extension tubes with my D5000 with 70-300mm lens for macro shots. I know its crazy big but it gives me a long working range and since you can get so far away you can use flash if you have to. I have a set of three tubes 12, 20 and 36mm. I use them all stacked and put the lens into manual mode. I pre-focus with zoom and then move the camera to get final focus. I have had pretty good results with this rig … but it is foolishly big. I notice this site changes my images and strips the EXIF so I will link images when I can.
Here is an example of using the flash. I am going to link to the original in hopes that when clicked on you can see the original … I have been trying hard to get picks of this guy. He/she is camera shy though and each time I try to get a shot it darts to the underside of the flower. I was getting a warning in this shot with the outstretched legs trying to make its tiny self bigger.
If you click on this image you can check out the eyes