I don't understand what surprises you. The memory load depends in large parts on the work requirements, I'd guess.
2 weeks ago I went from 4 GB to 8 GB (still would love to have more) here at work, because 4 didn't cut it and lead to lots of paging.
Visual Studio (often 2 or 3 instances, grabbing around 300-500 each)
MS SQL Server
IIS
OCR Engines (depending on load)
With Windows 7 as host (already not a slim OS) this killed my productivity with 4 GB, especially if (to get back on topic) I opened my beloved Firefox...
I've easily burned through 8GB of memory when I'm crunching numbers on large-ish datasets in Octave. (And through twice that when I had a bug in said Octave code...)
In my stack eclipse + tomcat hits up to 1300mb, plus leaky firefox with another 1gb, and windows and everything else at about 1.5gb. 4gb is barely enough.
2 weeks ago I went from 4 GB to 8 GB (still would love to have more) here at work, because 4 didn't cut it and lead to lots of paging.
With Windows 7 as host (already not a slim OS) this killed my productivity with 4 GB, especially if (to get back on topic) I opened my beloved Firefox...