Yes. The lack of WYSIWYG in Hammer is really annoying (my biggest bitch about it). However, considering it has to compile the lighting (and the light maps can take a very long time to compile), lighting in the editor may not be possible. I wish they'd at least have some basic lighting or something. No shadows, just radial lights to get an idea. I did hear a rumour that the final hammer (in the HL2 SDK) will have lighting in the editor, but i wouldn't hold my breath for this rumour to be true.
The displacment editing is very interesting. Was a bit disappointed by it at first, but it seems to be more useful than unreal's or far cry's terrain. For a start you can easily just create it from any brush (it's not so football-in-the-groin painful to set up as Unreal's) so you can have small 'terrain' easily placed in a small area. You are limited to 2 textures blending, but with how you can create multiple displacment brushes and sew them together, you can get away with more. As well as get better looking walls or cliff faces by having a seperate displacment brush with a seperate texture so it doesn't look like just a texture blend as the case with unreal's. You have a lot more control over the vertex editing as well. Also the poly count seems like it will need to be a lot lower as it wouldn't have FC-like terrain LODing. Speaking of which, does Unreal terrain LOD?