I've been using a fuel additive, made by Nulon (cannot remember it's name - costs about $15 for a litre) for the past two years with premium unleaded and have had no problems.

$15 for peace of mind is worth it in my books - and a bottle will last you close to a year if you fill up once a week.

The only thing that I have noticed is that my plugs seem to foul a bit quicker than before... can anyone shed any light on that one for me?