I love the look of the star destroyers. Nice work so far. Booleans, as Jay said, cause problems for me at a few pionts. Mostly during rendering you start to get ugly artifacts. Also the polycounts gets huge because the geomtry gets really slivered in spots. It looks clean at first but show all edges on the geometry and you will see what I mean. Also you should add bevels to all edges to avoid the paper cut look with advanced lighting and to help bring out the geometry. This is the maiins spot the bad geomtry starts to show. There are times you will nead to use it, if time is of the concern and the part you are modeling is a side peice that is not important. Crunch for the client that wants if fast and for a cheap price, then they do not get quality. If you are trying to show off modeling though it is not a good idea.