Let's not get into a Mac vs PC argument (it will never end). They both have their good and bad points.
As for the 10% argument... First, I think more like 5%. Second, true hackers and virus writers don't do these things to hurt the largest number of people possible. They do it to do something no one has done before. The "big" email virus were done because nobody had managed an attack at that level, plus they produced nice zombies. The Mac market is small, but it is also shining brightly. That it has only been attacked in small ways speaks volumes for security.
Macs do crash and lockup, particularly pre OS X. Not that I have had many, but every crash and lockup I have had since X was due to an application. Usually just the program dies. My current uptime is over 30 days.
Note: I said nothing negative about PC/Windows in this post. But I do have one major complaint about Macs. I can not download my dive computer to my Mac. I have a PC box just for this purpose, though I am thinking about reverse engineering the data stream.