this site has a lot of good
info...http://www.sql-server-performance.com/article_print.aspx?id=1216&type=art
On cache hit ratio:
SQL Server Buffer: Buffer Cache Hit Ratio
This SQL Server Buffer: Buffer Cache Hit Ratio counter indicates how often
SQL Server goes to the buffer, not the hard disk, to get data. In OLTP
applications, this ratio should exceed 90%, and ideally be over 99%. If your
buffer cache hit ratio is lower than 90%, you need to go out and buy more RAM
today. If the ratio is between 90% and 99%, then you should seriously
consider purchasing more RAM, as the closer you get to 99%, the faster your
SQL Server will perform. One thing to keep in mind about the SQL Server
Buffer: Buffer Cache Hit Ratio counter is that it is an average from the last
time the SQL Server instance was restarted. Because of this, you may want to
use the SQL Server Buffer: Buffer Cache Hit Ratio counter value found by
using the Performance Dashboard, which is described in a later article. This
counter is based on current activity, not average activity.

In OLAP applications, the ratio can be much less because of the nature of
how OLAP works. In any case, more RAM should increase the performance of SQL
Server.

Sreeji, How can i check the Cache Hit Ratio?