Outside US, it is a very small number.
In the other southern countries, I seldom know anyone with budget for Macs, unless they happen to work for some cool startup.
I do enterprise consulting across Europe and usually the guys with management positions are the ones with glowing Apples.
Furthermore the computer is a cost so it lowers the taxable income. According to our fiscal laws if you lease something (somebody does that with computers) then it is completely a cost. If you buy it, you can deduce only 20% per year over 5 years. This doesn't apply to goods sold for less than € 500.
Small companies are starting to buy Macs as well. Probably the boss can't have the face to keep a Mac for him/herself and give Windows boxes to the developers :-)
Large companies tend to stick to Windows PCs but they are becoming less inflexible. Again, people used to iPhones started to think that they could work with Macs as well and so it's starting from the top there too.
I think it's less about salary (except to some degree of course) and more about culture. When I do consulting for corporations I also only see Microsoft and HP or IBM, whereas even somewhat struggling freelance graphics designers or developers will have macs.
