I purchased one a while back, and it's been good.
Can do multi storey, furniture, bathrooms etc.
Here's a link to the latest version of it.
3D Home Architect
There's also a suite of the same which has more features again, and landscaping.
3D Home Architect Suite
Its easy to use, and produces pretty good results.
I dont know if there's a demo around.
I've used this to design complete homes, and modification to existing. It's not autocad, but then this is usable
Seriously though, I looked around, and you're right, lots of junk around. I bought this after lots of research (5 years ago now), and have never regretted it. Still use it (same version) now when I need to.
STANDARD features to look for.
Furniture
Cupboards - including overhead, sinks, ovens etc
Fixtures - Showers, Basins, Sinks, etc
Windows - styles, size
Doors - Styles, size
Multi storey - how many ?
Wall thickness - does it handle multiple?
Roof designers
Stairs
3d Views, helicopter views etc
Exportable to (DXF?) for architects
Electrical overlays
Room detection and naming
EASE OF USE
etc
Good Luck.
Simon.
ps. Did some looking into it, and it appears latest version has a new engine, so I'm not sure if it's as easy as mine was.
Check out
http://www.b4ubuild.com/links/cadd.shtml
further edit - Hmm. reading further, v5 of this is completely different to v3 like I have, or v4. V5 gets a lot of bagging. maybe get an older version from somewhere...