I've never worried about security issues with my Macs, and I don't think they're a significant problem.
This is a judgement call.
However, with apple pushing gatekeeper (it has been backported to 10.7) and removing Java from the base install, I don't believe they share your optimisim (neither do I).
The mac isn't a tiny share of the market any more and it is becoming more worthwhile to write exploits for.
Waiting until you get hacked (and potentially have your identity/bank details sniffed) is an interesting perspective. No one ever thinks they'll get hacked, until they do.
This isn't an apple-fud thing. I've been pushing our users here to get off XP (i'm an enterprise network admin by day) as soon as possible too - because it is simply lacking a lot of newer security features available in Vista, 7 and 8.
Exact same reason I believe people should be looking to get off Snow Leopard; upgrade to ML or Lion, or
plan their migration strategy to an alternative platform with support now.
Right now, whilst still supported - you're fine. But when support runs out, you need a plan. Whinging about how you hate the new OS and refusing to upgrade isn't really going to work out forever.