Locking pages in memory is definitely something to consider enabling if you are seeing Windows trim the working set from SQL Server. If this were happening you would see sudden drops in Page Life Expectancy (PLE) as well as entries in the SQL Error Log saying as much. There is a great debate on the topic of whether to enable it by default on x64 systems. Personally I only enable it if I am seeing the specific behaviors I mentioned but someone I respect a lot has written a great article on ths topic and cautiously recommends (if you monitor your server memory use very closely) enabling it by default:

Great SQL Server Debates: Lock Pages in Memory by Jonathan Kehayias, 12 December 2011[/url]

That said on the general debate, on Server 2003 running SQL 2005 memory trims imposed by Windows were much much much more prevalent than they are on SQL 2008+ on Server 2008 R2+.