In general, keeping auto update statistics is a good idea. There is a good article that you should read. The article discusses how autostats work and also discusses certain situation where autostats may not be a good idea.
INF: How SQL Server 7.0 and SQL Server 2000 Autostats Work
http://support.microsoft.com/default.aspx?scid=kb;en-us;195565
Yih-Yoon Lee
lee@yihyoon.com