I think that in general people who have already bought ipads will tell you that it won't be updated until next year. People who decided to wait will say before Christmas. I own one so I believe that it won't be until next year. I get the humour of that, so I'll tell you why I believe that it will be next year.
1, Unlike what Miles said most apple consumer products are on a yearly cycle. iPhone, iPod touch, iPod nano, iPod classic and most of the time the iPod shuffle. Vs the iMac, Mac mini, MacBook. In short if the word Mac is not in the title it is probably on a yearly cycle.
2, Everyone who says that it will be updated use the iPhone's launch as an example. However the only difference that apple made to the original iPhone was an increase in storage and a drop in price. Apart from storage the features of the phone did not change within the year. Adding the retina display or a camera is a bigger feature change than just adding storage.
In short I believe that an increase in storage for the iPad and a reduction in price, are unlikely but possible. But I would be very surprised if any other features were added to the iPad before March of next year.