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For doing mostly 2d work Vectorworks is by far the best CAD program in my opinion. It doesnt behave as "bureaucratically" as autocad. The plans also end up looking nicer and have better graphics or layouts. But for 3d its bad. If you want to do 2d as well as extensive 3d work, you better think about using a seperate programme for each, for example form-z for the 3d part and vectorworks for drawing sections and plan. Archicad is also good and has reasonable 3d capabilities.
 
If you only need 2D then PowerCADD is great. I am just starting to learn to use it and I find a lot of the features very helpful for my particular brand fo drafting (patent illustration). They have a free 30 day trial version if you want to give it a go. It is a little confusing at first but the documentation is pretty helpful.
 
Autocad

I seem to remember Autocad's developers being open to an OSX based version of the software and had a feedback form. There didn't seem to enough demand for the product so they trashed it. Also, it was felt that the Autocad interface was too windows like, so what would have been the point? Too bad for them, it would be so cool to have a nice Mac interface and a Dual G5. Oh well.
 
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