I see that the Activity Monitory shows a variety of information about System Memory usage. Are their particular values or perhaps ratios that would indicate with certainty that I need to upgrade my RAM?
At this moment, I'm running more than I usually do. I've got a couple of virtual machines running, several resource intensive development tools, three different browsers (Chrome, Firefox, and Safari), Mail, a database application, and a productivity tracking application. Normally, I run about half of those simultaneously. I have 4GB of RAM installed, and the Activity Monitor reports that I have:
Free: 518.5 MB
Wired: 1.08 GB
Active: 1.84 GB
Inactive: 587 MB
Used: 3.49 GB
VM size: 155.62 GB
Page ins: 1.08 GB
Page outs: 792 KB
Swap used: 16.7 MB
I know it is "only" about $90 to upgrade, but I see no point in spending money unless I truly acquire new capabilities or a notable increase in performance.