like F-stop junkie mentioned there are two different styles of ring lights. I dont do enough macro photography on land to make it justifable to get one, (UW is a different story, but i use a 3 strobe setup for that).
Now when if comes to using a ring light for portraits(not the family style either, but more glamour and high fashion) thats a different story its because im going for a shadowless look in the image to go along with flawless skin and/or high detail make up work (IE fantasy,etc). I have used a few brands of ringlights including several very expensive european brands but I use a
Alienbees ringlight and various modifiers from bare bulb to
50" softbox attached.
In general a ring light is of limited use to the average shooter when compared to a hotshoe mounted using on or off camera techniques for portraits.