ah... holes as in not some flaw in the bsp system that can create errors in some mathematical conditions, but the users not able to keep track of where they put their brushes and vertices and stuff?
::edit:: ah maybe not...
http://wiki.beyondunreal.com/wiki/BSP_Tree
like, when i use a bsp terrain, i make it so that its the only addition brush within that volume, and make it fit its subtraction brush perfectly... you can edit the vertices on the meshy side to create more convincing terrain
but i think the even better way is to use the bsp terrain as a subtraction, thats why the meshy side faces downwards... that way, the bsp terrain tool is more like 'the space above your bsp terrain' tool...
but i think i will use the bsp terrain to create arbitiary bsp shapes where its like just one big rock that is jutting out on a flat desert plane or something...i can shape them like terrain, yet move them around like other bsp brushes, that's got to be a good thing...
there are other concepts that i still want to know , tho, like since bsp is gonig to be slower , i want to know about this zoning concept, like antiportals and stuff