I think there are three things that could help it take off: 1) Allow boxed software. For example: Pages, Numbers, Keynote in one iWork package; or the Microsoft Office suite. 2) Allow demos! Either X days or Y hours of using the app. 3) Introduce mass-software purchasing for schools and businesses.
Not every ship hits an iceberg, but it's best to be protected with a double hull in case you do.
Personally, I would recommend either Sophos or ClamXav. I use Sophos on my iMac, although it decided it didn't want to work on my MacBook Air.
But for a small enterprise, I would recommend Sophos.