Well, there are some glitches with older versions of dnn - but I've got three clients that have a mac, we run the catalook store as well, and they upload their database of thousand of products every single day - the only issue we really ever had was administrators using Safair and when they switched over the editor was fine.. that's been the main issue I found in the past with Macs.
However, on older sites - I agree, there were issues with the solpart menu, but that I believe was fixed.
I know it runs well with Mac systems - because I had to endure 5 months of anal retentive Mac designers who nit picked everything they could possible think of to get the design as per their pixel perfect screen - and while it was a challenge at times, and we thought - hey we don't want to meet them in a dark alley one day - when the job was finally completed, they really loved it - and so do we... we're all friends again.
And with the shopping cart and the website administrator running Foxpro to manage the products - I thought .. oh no, this will do us in now...and yet, they've been running for 16 months without any issues, except when they want to edit the site and can't see the editor -switch back to Firefox and they're fine.
I also have another client who runs an online magazine with over 10,000 articles update daily, and we've just installed another build for them, with the blogs module, and so far, nothing but praise... they are very happy...and Mac owners, so don't despair - here are my tips.
Get rid of solpart menu - use a CSS friendly one - the only one we use is http://www.snapsis.com - each site has that on there - in fact, we don't use any of the dnn menus at all - they haven't kept up with what's on offer in the 'menu' world when it comes to speed and useability.
Get your administrators to use Firefox if they are administrating in a Mac
Get you skin updated perhaps and if the users don't have a Mac - get them to install Safari for Windows - sure it's not as advanced as Mozilla engine, but it will give you a close relationship to how a Mac viewer sees the site. We had to make some changes to websites when we looked through the eyes of a Mac, and have to respect that they too deserve and can get a decent viewing experience, but the person who manages the design may need to tweak and touch a little more.
Hope this helps - and yes you can win the war! Love your site - but we love our bikes too!
Nina Meiers