How right Youme is...
Displacements are a gift and a burden, I have a massive cliff and loads of tunnles in the map I am making. Displacements make it easy to get the shape that I want but because I am such a perfectionist I have done each of the 10,000+ nodes individually. Taken ages, but when it is finished it will probaly (I hope) hold up to even Youme's critical displacment eyes.
I guess what I am trying to say is, you need to play with it but don't go over the top. Valve maps have displacement errors that you have probably never noticed so a small fault here or there wont get noticed. If you do spend ages on them just remember they will probably not be noticed and only do them to your level of satisfaction not anybody else's after all it's your map.