Anytime cavebuddy. I forgot to mention that the cubemaps should be placed at least 64 hammer units off the ground. Also should have 1 where ever lighting changes. Although you shouldn't go crazy with them. Can't just have 1 cubemap either. Specially if you have many reflective textures.
Reflective textures (as I understand it) use the closest cubemap to them to generate the image that is reflected off it's surface. Each cubemap makes 6 pics (top,bottom and 4 sides) that make the 360 degree image in the reflection. Not all reflective textures reflect 100% of the cubemaps image, Like they all aren't perfect mirrors, but they need em even for that extra little shine.
Also, I'm guessing that the reason we have to build cubemaps ourselves, has something to do with needing the map compiled first. So it can generate the pics of the finished map. Would look weird if it built cubemaps of how the map looked in the editor.
Well I rambled on long enough, good luck with your map.