Long story short, I inherited an older sql server.
Its running 2003 Server Entperise, but has SQL 2008 standard installed. At the time of acquisition it had 4gb of ram and 8 SQL instances installed.
It also had terminal services installed on it with people occasionally logging into it to run GIS applications which were dependent on SQL
For the time being, lets ignore all of the bad practices since I can't change this around for the next few months due to work flow.
The default instance would generally grab ~1.5 to ~2gb of ram and all of the others would suffer with whatever dregs they could snag.
I chucked 16gb of ram in the box, made sure /pae settings were set in the boot.ini, configured awe memory settings in sql, etc.
Now the SQL instances will only use ~170mb of ram. Performance is no worse, and maybe a little better, but I'd like SQL to actually USE the ram we've installed.
Note the server is using more ram, but I think a lot of it is going towards terminal sessions.
Its currently using ~9gb of ram, has 10gb of page file in use and has all 8 sql instances using ~150 to ~170mb of ram.