Mark raises an interesting point, lighting is the key to great macro photography.

In fact getting too close can sometime actually cause problems by casting your own shadow on your subject, hence the advantage of using a 100mm lens over a 50mm to allow yourself to get a little further away.

I personally use macro tubes, but every time I use them I lust after Canon's 100mm (or even 135mm) Macro lenses. Just yesterday I was taking a picture of wedding rings and thought I'd really like a proper macro one day. The tubes take a little bit of light away from you, so you have to bump your exposure, it's not a lot but the more tubes you use the more you have to bump. Not ideal when you are shooting handheld macro

Many Macro photographers will set their focus manually then actually move the camera in and out a little for fine tuning, I tend to do this as well. I take my shots on a glass table usually (cool reflections of the rings!) I rest the front of the lens on the glass set my focus then simply slide the camera in and out until I'm happy with the shot, normally at f8 with a little help from some bounced flash.

Cheers

Cris