There is no doubt that the Mac and Linux markets are both growing. I imagine that if DoubleCAD could run on these platforms then DoubleCAD would be effortlessly be amongst the top CAD contenders amongst MAC and Linux users.
I feel that Mac users would more willingly part with money. There are some very clear an indisputable reasons why an increasingly large percentage of power users choose Mac. I say indisputable because that market is growing even though macs are quite expensive comparatively
as Unix Admin, who manages a network of 300 Windows PC's for the school where I work however at home where I have four children who use Apple Macs and I seldom get called by my family to deal with issues on the Mac.
So back to the topic: To the developers of DoubleCAD: I suggest that as a distant cousin to TurboCad and other products which do run on Mac. - Don't stray too far way from Mac and Linux worlds with your code base, because if you are successful getting DoubleCAD running on Apple Mac then it's a fairly trivial task to continue that journey over to Linux and you might capture a very wide audience since you have an outstanding product.
Another observation: Steam, the popular games engine http://store.steampowered.com/
have taken quite seriously the Apple and Linux market and now there are now an amazing number of Game titles flowing over into the Mac world with the Linux version of steam due for release in 2011. - this removed the argument that games did not run on Apple!
Many open source products run on Mac Linux and Windows for example Audacity, VLC's VLPlayer, Mozilla Firefox, Evernote, Dreamweaver, FileZilla, Skype, - and thats just some of the stuff on my Mac.
Microsoft and Google have both taken seriously the Mac and Linux markets, Microsoft have demonstrated this in the form of Litigation and Legal wrangling while Google continued to developed great software for example Google SketchUP and Picassa. - Although Microsoft do have a array of products which run on mac now. Too little too late in there case, but in yours there's still time
I suppose what I am saying is that it would be great if I could use DoubleCAD on my Mac and Linux computers