Antivirus software really isn't all that necessary right now. However, don't be surprised to see people trying to attack Android phones and iPhones in the near future. Every OS, whether its Linux, Unix, Windows or any other flavor of OSes out there, are vulnerable to attack. Anything that accesses the internet can be attacked.
With that said, the biggest issue that people should be concerned about is identity theft. Getting a virus on your computer is not that big of a deal, just factory reset your phone, done! However, if you download that cool wallpaper from the market they could gather information from your phone and send it all to a server in China, sound familiar?
I'm in the IT field and deal with security issues just about every day. Its not just about infecting a computer or a device anymore, its about getting as much information off that device and selling that information to other people. You'll still have the script kiddies who just want to cause trouble but the hardcore attackers are out to make money.
Protect your information on your phone and be VERY cautious on what you download. You may think that they only got your name and phone number off your phone, great... but then they find your facebook name and grab more information, then they go to your linkedin page and get even more. The more information you expose on the internet and your devices the easier it is for attacker to collect data.
One last thing, don't be fooled or think your safe because you don't use a windows device (either a smartphone or computer) because if they want your information, they will get it. Its not about getting a virus, its about getting your money. There are so many scams on the internet that they don't even need to infect your computer these days.