I'm Reviving These Forums
Because someone said to do so. These forums don't seem dead, and a post by me isn't going to do anything. Regardless, I am posting.
P.S. I can map now, trust me. I know how to use every tool (except Carve) and every entity (including brush entities like func_rotatings).
Keep on doing whatever it is you do, I'll get back to making personal maps for HL2 and playing Black Mesa.
Think of all the things we learned
For the people who are still alive
By far the best way to use the carve tool: Don't 
What exactly is the carve tool? I guess its probably good I don't know about it, but what's so terrible?
Its an inefficient version of the clipping tool, but thats only true for shapes like octagons. Nacimota has a guide on the Carve tool, theres a link about it on the bottom of the Carve Tool's page on the VDC. He says its good for making rectangular holes, which are pretty much the only holes in Portal 2 mapping.
Think of all the things we learned
For the people who are still alive
She
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In theory carve tool is amazing; you let two brushes intersect and the carve tool carves a hole in the surface.
In 99.95% of the cases however it goes wrong. The algorithm often makes bad decisions, with can give:
* Problems when re-scaling your brush.
* Microbrushes
* Wrecked up visleaves.
The clip tool can do precisely the same, but it requires a few more actions. it does give you a lot
more control though. If you can handle the clip tool, you should totally use that rather then the carve tool. If you can't handle the clip tool, stop now and learn to use it. Don't come back before you know how to use it.
She
What's the big deal mslipper?
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In theory carve tool is amazing; you let two brushes intersect and the carve tool carves a hole in the surface.
In 99.95% of the cases however it goes wrong. The algorithm often makes bad decisions, with can give:
* Problems when re-scaling your brush.
* Microbrushes
* Wrecked up visleaves.
The clip tool can do precisely the same, but it requires a few more actions. it does give you a lot
more control though. If you can handle the clip tool, you should totally use that rather then the carve tool. If you can't handle the clip tool, stop now and learn to use it. Don't come back before you know how to use it.
This is the example I usually give, taking carving to the extreme: http://i.imgur.com/yqGm5.png
That is four spheres carved into each other. The blue lines in the 3D view are the edges of visleaves.
Nacimota used to have a fantastic article about it on his website but it's currently down. 
I see what you did there UsCubra11.
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I know how to use a hammer and a screwdriver, but that doesn't mean I can build a good house hehe
you should totally check out this amazing video on youtube:
http://www.youtube.com/watch?v=xh9Kr2iO4XI
If you manage to actually compile a map with terrain that is made with this method we will probably ban you 
terrain -> displacements.
Cutting stuff from other stuff -> clip tool.