I recently posted some data about applications taking up the most RAM on my laptop. That was after 9 days of uptime, while this is after 12 hours:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
16033 root      20   0  527m 109m  11m S    3  5.5   6:52.82 Xorg
17834 mg        20   0  244m 105m  24m S    6  5.3   3:26.49 firefox
26425 mg        20   0 96872  58m  12m S    0  2.9   0:01.71 evince
16747 mg        20   0 90704  54m  19m S    0  2.8   0:10.70 tomboy
27169 mg        20   0  166m  53m  23m S    0  2.7   0:07.05 banshee-1
27167 mg        20   0 77392  31m  17m S    0  1.6   0:01.16 pidgin
16706 mg        20   0 86508  27m  18m S    0  1.4   0:35.35 gnome-panel
16708 mg        20   0 75196  20m  14m S    0  1.0   0:02.80 nautilus
20092 mg        20   0 61880  19m  11m S    1  1.0   0:07.08 gnome-terminal
16614 mg        20   0 58456  15m 9836 S    0  0.8   0:09.82 gnome-settings-

I don't have GNOME Do any more, and I've only one of the two PDFs open in Evince. I don't see multiload-applet on the first page of top output, which seems to indicate a slow leak. Evince has the same two documents. That concept doesn't quite apply to Banshee or Pidgin, but Pidgin's numbers are quite striking anyway (from 70 megs VIRT to 1.6 gigs VIRT in 9 days; thankfully RES only grows 2x during that time).

OS: Ubuntu 8.10, up-to-date with all the updates from -security, -updates, -proposed-updates and -backports.

Incidentally, I have 12 hours of uptime because my battery died while the laptops was suspended during my flight back home (either that, or it work up in the backpack, which is a scary thought). Apparently Ubuntu tried to hibernate when the battery was very low, which was a nice gesture. This didn't work out so well when resuming, since the kernels didn't match -- I had installed a kernel update, but hadn't rebooted. I don't think I ever used hibernation successfully in Linux.