If it's not cracked and it doesn't have a flat spot, it's really just more annoying than unsafe I would say... You don't need to spend $400 either, http://americanmototire.com has good prices shipped and you don't need to stay with a stock brand. I run IRC up front and Michelin in the rear. Read some tire threads here, we have as many opinions on them as we do brands of oil

Always remember to be yourself. Unless you suck. Then pretend to be someone else.