they system went public yesterday. I used it and it worked great. You first pick an area you want (epcot, etc). You can then select a specific restaurant. You plug in the date or date range and the time you prefer.
It gives you times available and you select one. If the restaurant is not available for your time (and within 30 minutes or so each way) then there are other choices given.
You select one and then it gives you a confirmation number! Easy!
if you go to the disney dining board you will see lots of posts about this topic.