Variable rates do influence fixed rates, but the funds aren't from the same source, so even if the RBA drops 50 points, it doesn't mean the fixed will drop as well. Of course this also means that variable could stay the same and we'll see the fixed rates drop.
Currently fixed rates are below the long term variable rates (which tends to be around 7%) so fixing now could save money. On the other hand with the Euro in trouble, the long term rates could drop, which means that todays low rates night be tomorrows high rates.
Generally I'd say fixed rates are best considered so you know what your repayments will be for a period of time. They're best used as a risk management strategy. Fixing right now might save money, but there's no guarantee of this. If you do decide to fix and rated do drop further, look at it and consider that you might not be on the best rates, but at least you know what you're paying.