From experience OS/X guzzle memory like no other OS I know.
MBP here with two browsers open 24x7 plus whatever other stuff I have open (avg 4-5 open windows).
Here's the output of my 'uptime' command:
14:59 up 6 days, 14:14, 2 users, load averages: 0.22 0.34 0.54
Here's the top of my 'top' output:
Processes: 60 total, 3 running, 57 sleeping, 319 threads 15:01:50
Load Avg: 0.35, 0.35, 0.51 CPU usage: 4.5% user, 5.1% sys, 90.93% idle
SharedLibs: 8988K resident, 1988K data, 0B linkedit.
MemRegions: 26148 total, 927M resident, 22M private, 454M shared.
PhysMem: 854M wired, 2181M active, 525M inactive, 3560M used, 408M free.
VM: 134G vsize, 1036M framework vsize, 928794(0) pageins, 150(0) pageouts.
Networks: packets: 11435804/7468M in, 10101665/1550M out.
Disks: 1329934/17G read, 604685/24G written.
Seems pretty healthy to me. If you want to point fingers, try firefox (currently using 723 MB real) or itunes (currently using 275 MB real). That just blows my mind. Two of the (ostensibly) most basic programs using more RAM than would fit into my first hard drive.