Welcome to CB. I wasn't sure if I wanted to get a Bold because I really like my Curve -- it seems like its made for my hands. But after eading about what a 3G device will do, I can't wait to get my hands on one.
Besides the 3G, Bigger Screen, More memory, faster processor as everyone is stating. The Bold also has something the curve does not have both GPS and Wifi on the same model. The curve has either GPS *8310* or Wifi *8320* where the Bold is the 9000 with both!
What if we already have 3G? The 1G on board memory will be nice, but maybe a little overkill. It is going to be hard for me, like exelant said, it was made for my hands. Can't wait to see it and play with it a little. The Curve is such a nice device, it is going to be hard to believe that the Bold will "blow" it away.