Great Product! I've been using the free version for a while and I really like the improvements in the 'professional' package.
There's just one thing I'd really like to see. The ability to switch on & off groups of layers, so that different but related parts can be developed in the same file. Interactions can be checked. Crucially, changes common to several parts because they share a common layer are virtually instant and fool-proof. (An important consideration when I'm on the design team!)
I believe another common but over-priced CAD package has this facility, but was suprised to find that you can't restore two or more states simultaneously - amazing! This is your opportunity for a bit of one-upmanship. I believe that this information is stored in the DXF format.
Thanks again for QCad.