Hard to say if it's isolated to your email or not, viruses can do really nasty things to hide in your system, if you have a single specific target and it's not that hard to make something undetectable if you got the resources. Then it's just a case of getting it inside the target.
In the case of preventing viruses everyone should have firewall, anti virus, Windows/Mac/Linux up to date, web browsers, flash, PDF reader, java up to date too.
Highly recommend PSI secunia, it's a program that checks what needs patching, Microsoft Security Essentials if you want a free easy to use anti virus, if you ain't got a firewall in your OS then there is a free version Zonealarm.
For a bit of security through obscurity I'd change Adobe Reader for Foxit Reader or PDF XChange viewer, also change Internet Explorer for Google Chrome. I use Firefox but market share has gone up yet I can't live without my addons, good addon for Firefox is noscript but it's complex, fiddley, especially when it's a fresh install.
As for facebook, I'm on it, piracy settings at the maximum, absolutely refuse to use any of the third party applications on there. Way too easy for anyone to add an application of dodgy code.
With passwords I use a mix of upper and lower case characters with numbers and symbols, and have different ones for my email and bank