They look at your credit utilization too. By not carrying a balance you actually hurt yourself a bit... or so I'm told.
To the OP, I would not waste my time to get the magic Fico of 850. If you are 800 and above (again, speaking as FICO only), then you are golden.
Urban legend. Not true. See below, directly from MyFico.com
MYFICO.COM 5 components score of credit
1.payment history = 35% Do not miss any payments or late. Ever.
2.amount owed = 30% 30% utilization or less, 10% is better.
3.length of credit = 15% The longer you have credit, the better.
4. new credit open = 10% Do not open new credit cards just for kick. Use it wisely.
5. types of credit = 10% Better if you have a variety of credit types but do not do it just for kick.