I dont have any trouble with virus on my Win workstation, if you dont leech 200KB exe files named World-of-warcraft-2-beta.exe chance of getting a virus on PC is not that big. Keep in mind I run IE also, it starts faster then FF and does not consume as much memory.
It is easy to get a virus when you hunt for pirated software, keep in mind piracy on the PC is industry standard.
Also, my 3 year old 4 core workstation with 4GB has never felt slow, I can have Photoshop up and running in the background all day long and find myself surprised that the system was not running slower with PS open with lots of projects, or PS + lots of other huge apps.
Best of all?
It cost me 500 euro and will probably last 3 more years (at least 5 more years, probably 10 more years if I dont care about games).
Yes it is not Unix, but honestly, Ubuntu is Unix too and it is free. Ubuntu is for my 8TB fileserver danke schön.
Be careful endorising Apple, next you know you need to pay for an app to start your system and you wont be able to copy a file if you dont jailbreak your hardware. App store soon integrated in OS, that is the future of $$$, thanks for Ubuntu there is a free future for workstation OS once MS goes on the appstore bandwagon.